Kaiser Aluminum (KALU) 10-Q 25 Jul 24 2024 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2024	Jul. 22, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2024
Document Transition Report	false
Entity File Number	1-09447
Entity Registrant Name	KAISER ALUMINUM CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	94-3030279
Entity Address, Address Line One	1550 West McEwen Drive
Entity Address, Address Line Two	Suite 500
Entity Address, City or Town	Franklin
Entity Address, State or Province	TN
Entity Address, Postal Zip Code	37067
City Area Code	629
Local Phone Number	252-7040
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Title of 12(b) Security	Common stock, par value $0.01 per share
Trading Symbol	KALU
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		16,087,112
Entity Central Index Key	0000811596
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q2
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS (UN

CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Millions		Jun. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents		$ 70.4	$ 82.4
Receivables:
Trade receivables, net		370.1	325.2
Other		13.4	12.4
Contract assets		63.7	58.5
Inventories	[1]	446.9	477.2
Prepaid expenses and other current assets		46	34.5
Total current assets		1,010.5	990.2
Property, plant and equipment, net		1,084.6	1,052.1
Operating lease assets		29.1	32.6
Deferred tax assets, net		6	6
Intangible assets, net		47.7	50
Goodwill		18.8	18.8
Other assets		119	117.7
Total assets		2,315.7	2,267.4
Current liabilities:
Accounts payable		281.8	252.7
Accrued salaries, wages and related expenses		48.9	53
Other accrued liabilities		65.7	64.3
Total current liabilities		396.4	370
Long-term portion of operating lease liabilities		26.3	29.2
Pension and other postretirement benefits		77.6	76.8
Net liabilities of Salaried VEBA		3.8	3.8
Deferred tax liabilities		20.6	13.9
Long-term liabilities		88.3	81.7
Long-term debt, net		1,040.7	1,039.8
Total liabilities		1,653.7	1,615.2
Commitments and contingencies - Note 7
Stockholders’ equity:
Preferred stock, 5,000,000 shares authorized at both June 30, 2024 and December 31, 2023; no shares were issued and outstanding at June 30, 2024 and December 31, 2023
Common stock, par value $0.01, 90,000,000 shares authorized at both June 30, 2024 and December 31, 2023; 22,922,398 shares issued and 16,087,112 shares outstanding at June 30, 2024; 22,851,077 shares issued and 16,015,791 shares outstanding at December 31, 2023		0.2	0.2
Additional paid in capital		1,111	1,104.7
Retained earnings		12.5	10.1
Treasury stock, at cost, 6,835,286 shares at both June 30, 2024 and December 31, 2023		(475.9)	(475.9)
Accumulated other comprehensive income		14.2	13.1
Total stockholders’ equity		662	652.2
Total liabilities and stockholders' equity		$ 2,315.7	$ 2,267.4
[1] At June 30, 2024 and December 31, 2023, the current cost of our inventory exceeded its stated last-in, first-out (“LIFO”) value by $ 83.5 million and $ 56.0 million , respectively.

CONSOLIDATED BALANCE SHEETS (_2

CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Jun. 30, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	90,000,000	90,000,000
Common Stock, shares issued	22,922,398	22,851,077
Common stock, shares outstanding	16,087,112	16,015,791
Treasury stock, shares	6,835,286	6,835,286

STATEMENTS OF CONSOLIDATED INCO

STATEMENTS OF CONSOLIDATED INCOME (UNAUDITED) - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income Statement [Abstract]
Net sales	$ 773.4	$ 814.1	$ 1,510.9	$ 1,621.7
Costs and expenses:
Cost of products sold, excluding depreciation and amortization	690.5	718.4	1,333.4	1,449.5
Depreciation and amortization	29	26.4	57.8	52.7
Selling, general, administrative, research and development	31.6	32.2	64.2	61.9
Restructuring costs	6.8	1.2	6.9	2.6
Other operating charges, net			0.4
Total costs and expenses	757.9	778.2	1,462.7	1,566.7
Operating income	15.5	35.9	48.2	55
Other (expense) income:
Interest expense	(11.1)	(12.1)	(22.6)	(24)
Other (expense) income, net - Note 9	(0.5)	(2.5)	10.4	11.1
Income before income taxes	3.9	21.3	36	42.1
Income tax provision	(0.8)	(3)	(8.3)	(7.9)
Net income	$ 3.1	$ 18.3	$ 27.7	$ 34.2
Net income per common share:
Basic	$ 0.19	$ 1.14	$ 1.72	$ 2.14
Diluted	$ 0.19	$ 1.14	$ 1.69	$ 2.12
Weighted-average number of common shares outstanding (in thousands):
Basic	16,072	15,974	16,050	15,957
Diluted	16,398	16,083	16,321	16,090

STATEMENTS OF CONSOLIDATED COMP

STATEMENTS OF CONSOLIDATED COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Statement of Comprehensive Income [Abstract]
Net income	$ 3.1	$ 18.3	$ 27.7	$ 34.2
Other comprehensive (loss) income, net of tax - Note 8:
Defined benefit plans	(0.1)	(4.6)	(0.6)	(3.9)
Cash flow hedges	3.3	(2.7)	1.7	(4.5)
Other comprehensive income (loss), net of tax	3.2	(7.3)	1.1	(8.4)
Comprehensive income	$ 6.3	$ 11	$ 28.8	$ 25.8

STATEMENTS OF CONSOLIDATED STOC

STATEMENTS OF CONSOLIDATED STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Millions		Total	Common Stock		Additional Paid in Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2022		$ 631.2	$ 0.2		$ 1,090.4	$ 13.3	$ (475.9)	$ 3.2
Beginning balance (shares) at Dec. 31, 2022			15,940,756
Net income		15.9				15.9
Other comprehensive (loss) income, net of tax		(1.1)						(1.1)
Common shares issued (including impacts from Long-Term Incentive programs) (shares)			49,128
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued		(1.3)			(1.3)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued (shares)			(15,848)
Cash dividends declared	[1]	(12.5)				(12.5)
Amortization of unearned equity compensation		3.4			3.4
Ending balance at Mar. 31, 2023		635.6	$ 0.2		1,092.5	16.7	(475.9)	2.1
Ending balance (shares) at Mar. 31, 2023			15,974,036
Beginning balance at Dec. 31, 2022		631.2	$ 0.2		1,090.4	13.3	(475.9)	3.2
Beginning balance (shares) at Dec. 31, 2022			15,940,756
Net income		34.2
Other comprehensive (loss) income, net of tax		(8.4)
Ending balance at Jun. 30, 2023		638.1	$ 0.2		1,096.6	22.4	(475.9)	(5.2)
Ending balance (shares) at Jun. 30, 2023			16,013,164
Beginning balance at Mar. 31, 2023		635.6	$ 0.2		1,092.5	16.7	(475.9)	2.1
Beginning balance (shares) at Mar. 31, 2023			15,974,036
Net income		18.3				18.3
Other comprehensive (loss) income, net of tax		(7.3)						(7.3)
Common shares issued (including impacts from Long-Term Incentive programs)		0.7			0.7
Common shares issued (including impacts from Long-Term Incentive programs) (shares)			45,164
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued		(0.4)			(0.4)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued (shares)			(6,036)
Cash dividends declared	[1]	(12.6)				(12.6)
Amortization of unearned equity compensation		3.8			3.8
Ending balance at Jun. 30, 2023		638.1	$ 0.2		1,096.6	22.4	(475.9)	(5.2)
Ending balance (shares) at Jun. 30, 2023			16,013,164
Beginning balance at Dec. 31, 2023		$ 652.2	$ 0.2		1,104.7	10.1	(475.9)	13.1
Beginning balance (shares) at Dec. 31, 2023		16,015,791	16,015,791	[2]
Net income		$ 24.6				24.6
Other comprehensive (loss) income, net of tax		(2.1)						(2.1)
Common shares issued (including impacts from Long-Term Incentive programs) (shares)	[2]		56,416
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued		(1.2)			(1.2)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued (shares)	[2]		(16,175)
Cash dividends declared	[3]	(12.6)				(12.6)
Amortization of unearned equity compensation		4			4
Ending balance at Mar. 31, 2024		664.9	$ 0.2		1,107.5	22.1	(475.9)	11
Ending balance (shares) at Mar. 31, 2024	[2]		16,056,032
Beginning balance at Dec. 31, 2023		$ 652.2	$ 0.2		1,104.7	10.1	(475.9)	13.1
Beginning balance (shares) at Dec. 31, 2023		16,015,791	16,015,791	[2]
Net income		$ 27.7
Other comprehensive (loss) income, net of tax		1.1
Ending balance at Jun. 30, 2024		$ 662	$ 0.2		1,111	12.5	(475.9)	14.2
Ending balance (shares) at Jun. 30, 2024		16,087,112	16,087,112	[2]
Beginning balance at Mar. 31, 2024		$ 664.9	$ 0.2		1,107.5	22.1	(475.9)	11
Beginning balance (shares) at Mar. 31, 2024	[2]		16,056,032
Net income		3.1				3.1
Other comprehensive (loss) income, net of tax		3.2						3.2
Common shares issued (including impacts from Long-Term Incentive programs)		0.5			0.5
Common shares issued (including impacts from Long-Term Incentive programs) (shares)	[2]		38,143
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued		(0.6)			(0.6)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares/common shares issued (shares)	[2]		(7,063)
Cash dividends declared	[3]	(12.7)				(12.7)
Amortization of unearned equity compensation		3.6			3.6
Ending balance at Jun. 30, 2024		$ 662	$ 0.2		$ 1,111	$ 12.5	$ (475.9)	$ 14.2
Ending balance (shares) at Jun. 30, 2024		16,087,112	16,087,112	[2]
[1] Dividends declared per common share were $ 0.77 for the quarters ended March 31, 2023 and June 30, 2023. At June 30, 2024, 607,964 shares were available for awards under the Kaiser Aluminum Corporation 2021 Equity and Incentive Compensation Plan, as amended and restated Dividends declared per common share were $ 0.77 for the quarters ended March 31, 2024 and June 30, 2024.

STATEMENTS OF CONSOLIDATED ST_2

STATEMENTS OF CONSOLIDATED STOCKHOLDERS' EQUITY (UNAUDITED) (Parenthetical)	3 Months Ended
	Jun. 30, 2024 $ / shares shares
Statement of Stockholders' Equity [Abstract]
Shares available for awards (shares) | shares	607,964
Cash dividends declared (in dollars per share) | $ / shares	$ 0.77

STATEMENTS OF CONSOLIDATED CASH

STATEMENTS OF CONSOLIDATED CASH FLOWS (UNAUDITED) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Cash flows from operating activities:
Net income	$ 27.7	$ 34.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property, plant and equipment	55.5	49.9
Amortization of definite-lived intangible assets	2.3	2.8
Amortization of debt premium and debt issuance costs	1.1	1
Amortization of cloud computing implementation costs	0.6	0.7
Deferred income taxes	6.4	6.6
Non-cash LIFO charge (benefit)	4.5	(4)
Non-cash equity compensation	8.1	7.9
Non-cash asset impairment charge	3.6
Non-cash unrealized loss on derivative positions	2.2
Loss (gain) on disposition of property, plant and equipment	0.5	(14.2)
Bad debt expense	0.3
Non-cash postretirement defined benefit plan cost	4.3	6.4
Changes in operating assets and liabilities:
Trade and other receivables	(46.2)	(17.8)
Contract assets	(5.2)	2.3
Inventories (excluding LIFO adjustments)	22.6	(31.5)
Prepaid expenses and other current assets	(10.9)	(4.8)
Accounts payable	16.1	(56)
Accrued liabilities	(3.4)	2.3
Annual variable cash contributions to Salaried VEBA	(1.1)
Long-term assets and liabilities, net	0.6	(1)
Net cash provided by operating activities	89.6	47.8
Cash flows from investing activities:
Capital expenditures	(73.7)	(82.6)
Purchase of equity securities	(0.1)	(0.3)
Proceeds from sale of equity securities	0.2
Proceeds from disposition of property, plant and equipment		15.2
Net cash used in investing activities	(73.6)	(67.7)
Cash flows from financing activities:
Borrowings under the Revolving Credit Facility		210
Repayment of borrowings under the Revolving Credit Facility		(195)
Repayment of finance lease	(0.9)	(1.2)
Cancellation of shares to cover tax withholdings upon common shares issued	(1.8)	(1.7)
Cash dividends and dividend equivalents paid	(25.3)	(25.1)
Net cash used in financing activities	(28)	(13)
Net decrease in cash, cash equivalents and restricted cash during the period	(12)	(32.9)
Cash, cash equivalents and restricted cash at beginning of period	100.7	71.3
Cash, cash equivalents and restricted cash at end of period	$ 88.7	$ 38.4

STATEMENTS OF CONSOLIDATED CA_2

STATEMENTS OF CONSOLIDATED CASH FLOWS (UNAUDITED) (Parenthetical) $ in Millions	6 Months Ended
	Jun. 30, 2024 USD ($)
Statement of Cash Flows [Abstract]
Inventory write-down related to certain alloying metals	$ 3.2
Impairment charge on land held for sale	$ 0.4

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ 3.1	$ 24.6	$ 18.3	$ 15.9	$ 27.7	$ 34.2

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Jun. 30, 2024
Trading Arrangements, by Individual
Material Terms of Trading Arrangement	Rule 10b5-1 Trading Arrangements. During the quarter ended June 30, 2024 , no director or officer of the Company adopted , modified , or terminated a "Rule 10b5-1 trading arrangement" or "non-Rule 10b5-1 trading arrangement" as each term is defined in Item 408 of Regulation S-K.
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Rule 10b5-1 Arrangement Modified	false
Non-Rule 10b5-1 Arrangement Modified	false

Basis of Presentation and Recen

Basis of Presentation and Recent Accounting Pronouncements	6 Months Ended
	Jun. 30, 2024
Accounting Policies [Abstract]
Basis of Presentation and Recent Accounting Pronouncements	1. Basis of Presentation and Recent Accounting Pronouncements This Form 10-Q should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2023. Unless the context otherwise requires, references in these notes to interim consolidated financial statements - unaudited to “Kaiser,” “we,” “us,” “our,” “the Company” and “our Company” refer collectively to Kaiser Aluminum Corporation and its subsidiaries. Principles of Consolidation and Basis of Presentation. The accompanying unaudited consolidated financial statements include the accounts of our wholly owned subsidiaries and are prepared in accordance with GAAP and the rules and regulations of the SEC applicable for interim periods and, therefore, do not include all information and footnotes required by GAAP for complete financial statements. In management’s opinion, all adjustments (which include normal recurring adjustments) considered necessary for a fair presentation have been included. We have reclassified certain items in prior periods to conform to current classifications. The results of operations for our interim periods are not necessarily indicative of the results of operations that may be achieved for the entire 2024 fiscal year. The financial information as of December 31, 2023 is derived from our audited consolidated financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2023 . Use of Estimates in the Preparation of Financial Statements. The preparation of financial statements in accordance with GAAP requires the use of estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities known to exist as of the date the financial statements are published and the reported amounts of revenues and expenses during the reporting period. Uncertainties with respect to such estimates and assumptions are inherent in the preparation of our consolidated financial statements; accordingly, it is possible that the actual results could differ from these estimates and assumptions, which could have a material effect on the reported amounts of our consolidated financial position and results of operations. Accounting Pronouncements Issued But Not Yet Adopted Disclosure Improvements. In October 2023, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2023-06 (“ASU 2023-06”), Codification Amendments in Response to the SEC’s Disclosure Update and Simplification Initiative. The guidance amends GAAP to reflect updates and simplifications to certain disclosure requirements referred to the FASB by the SEC. The amendments in ASU 2023-06 will become effective on the date which the SEC’s removal of the related disclosure becomes effective. If by June 30, 2027, the SEC does not remove the related disclosure, the pending amendment will be removed from ASC 2023-06 and it will not be effective. Adoption of ASU 2023-06 is expected to modify the disclosure and presentation requirements only and is not expected to have a material impact on our consolidated financial statements. Segment Reporting. In November 2023, the FASB issued ASU No. 2023-07 (“ASU 2023-07”), Improvements to Reportable Segment Disclosures. The guidance primarily will require enhanced disclosures about significant segment expenses. All disclosure requirements under ASU 2023-07 and existing segment disclosures in ASC 280, Segment Reporting are also required for public entities with a single reportable segment. The amendments in ASU 2023-07 are effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024, with early adoption permitted. A retrospective approach is required to be applied to all prior periods presented in the financial statements. We plan to adopt the provisions of ASU 2023-07 in the fourth quarter of fiscal 2024 and continue to evaluate the disclosure requirements related to the new standard. Income Taxes. In December 2023, the FASB issued ASU No. 2023-09 (“ASU 2023-09”), Improvements to Income Tax Disclosures. The guidance is intended to improve income tax disclosure requirements by requiring (i) consistent categories and greater disaggregation of information in the rate reconciliation and (ii) the disaggregation of income taxes paid by jurisdiction. The guidance makes several other changes to the income tax disclosure requirements. The amendments in ASU 2023-09 are effective for fiscal years beginning after December 15, 2024, with early adoption permitted, and is required to be applied prospectively with the option of retrospective application. We plan to adopt the provisions of ASU 2023-09 in the fourth quarter of fiscal 2025 and continue to evaluate the disclosure requirements related to the new standard.

Supplemental Balance Sheet Info

Supplemental Balance Sheet Information	6 Months Ended
	Jun. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Supplemental Balance Sheet Information	2. Supplemental Balance Sheet Information As of June 30, 2024 As of December 31, 2023 (In millions of dollars) Trade Receivables, Net Billed trade receivables $ 370.9 $ 325.8 Allowance for doubtful receivables ( 0.8 ) ( 0.6 ) Trade receivables, net $ 370.1 $ 325.2 Inventories 1 Finished products $ 72.1 $ 89.3 Work-in-process 210.2 210.8 Raw materials 148.0 161.5 Operating supplies 16.6 15.6 Inventories $ 446.9 $ 477.2 Property, Plant and Equipment, Net Land and improvements $ 37.2 $ 38.0 Buildings and leasehold improvements 241.6 238.4 Machinery and equipment 1,279.7 1,265.3 Construction in progress 240.1 173.7 Property, plant and equipment, gross 1,798.6 1,715.4 Accumulated depreciation and amortization ( 715.5 ) ( 663.7 ) Land held for sale 1.5 0.4 Property, plant and equipment, net $ 1,084.6 $ 1,052.1 Other Assets Assets to be conveyed associated with Warrick acquisition $ 56.8 $ 56.8 Restricted cash – Note 12 18.3 18.3 Long-term replacement parts 17.3 16.7 Other 26.6 25.9 Other assets $ 119.0 $ 117.7 Other Accrued Liabilities Uncleared cash disbursements $ 20.0 $ 15.7 Accrued income taxes and other taxes payable 10.8 9.5 Accrued annual contribution to Salaried VEBA — 1.1 Accrued interest 9.9 9.9 Short-term environmental accrual – Note 7 0.5 2.8 Current operating lease liabilities 7.2 8.0 Current finance lease liabilities 2.5 2.1 Other – Note 5 14.8 15.2 Other accrued liabilities $ 65.7 $ 64.3 Long-Term Liabilities Workers' compensation accrual $ 29.7 $ 29.9 Long-term environmental accrual – Note 7 14.8 14.2 Other long-term liabilities 43.8 37.6 Long-term liabilities $ 88.3 $ 81.7 1. At June 30, 2024 and December 31, 2023, the current cost of our inventory exceeded its stated last-in, first-out (“LIFO”) value by $ 83.5 million and $ 56.0 million , respectively.

Employee Benefits

Employee Benefits	6 Months Ended
	Jun. 30, 2024
Retirement Benefits [Abstract]
Employee Benefits	3. Employee Benefits Deferred Compensation Plan Assets of our deferred compensation plan are included in Other assets, classified within Level 1 of the fair value hierarchy and are measured and recorded at fair value based on their quoted market prices. The fair value of these assets at June 30, 2024 and December 31, 2023 was $ 11.5 million and $ 11.1 million , respectively. Assets in the trust are held in various investment funds at certain registered investment companies and are accounted for as equity investments with changes in fair value recorded within Other (expense) income, net (see Note 9). Offsetting liabilities relating to the deferred compensation plan are included in Other accrued liabilities and Long-term liabilities. Short-Term Incentive Plans As of June 30, 2024, we had a liability of $ 8.7 million recorded within Accrued salaries, wages and related expenses for estimated probable future payments under the 2024 short-term incentive plans. Postretirement Benefit Plans The following table presents the total expense related to all postretirement benefit plans (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Defined contribution plans 1 $ 4.2 $ 4.3 $ 10.0 $ 10.1 Deferred compensation plan 2 — 0.4 0.7 0.6 Multiemployer pension plans 1 1.5 1.4 3.0 2.8 Net periodic postretirement benefit cost relating to defined benefit plans 2,3 2.8 3.3 4.3 6.4 Total $ 8.5 $ 9.4 $ 18.0 $ 19.9 1. Substantially all of these charges related to employee benefits are in COGS with the remaining balance in Selling, general, administrative, research, and development (“SG&A and R&D”) within our Statements of Consolidated Income. 2. Deferred compensation plan expense and the current service cost component of Net periodic postretirement benefit cost relating to Salaried VEBA are included within our Statements of Consolidated Income in SG&A and R&D for all periods presented. All other components of Net periodic postretirement benefit cost relating to Salaried VEBA are included within Other (expense) income, net, on our Statements of Consolidated Income. 3. The current service cost component of Net periodic postretirement benefit cost relating to both the pension plans and the OPEB plan are included within our Statements of Consolidated Income in COGS for all periods presented. All other components of Net periodic postretirement benefit cost relating to both the pension plans and the OPEB plan are included within Other (expense) income, net, on our Statements of Consolidated Income. Warrick Pension Amendment. During the quarter ended June 30, 2024, we amended the Kaiser Aluminum Warrick pension plan (“Warrick Pension Plan”) to clarify certain plan provisions going back to the date of our acquisition of Warrick, which resulted in an interim remeasurement of the Warrick Pension Plan as of June 30, 2024. The remeasurement decreased the Warrick Pension Plan’s net funded status by $ 0.8 million, driven by: (i) a $ 2.2 million increase in pre-tax prior service cost, which we recorded to AOCI and is expected to be amortized on a straight-line basis over approximately 10 years , and (ii) an actuarial gain of $ 1.4 million, reflecting an increase in the assumed discount rate. The discount rate assumption used to determine the Warrick Pension Plan benefit obligation was 5.51 % at June 30, 2024 compared to 5.04 % at December 31, 2023. There was no change to the expected long-term rate of return on plan assets assumption at June 30, 2024 compared to December 31, 2023. The Warrick Pension Plan amendment had no effect on our expected contributions for 2024. During the six months ended June 30, 2024, we contributed $ 3.6 million to the pension plans. We expect to make further contributions of approximately $ 2.2 million to the pension plans during the remainder of 2024. Components of Net Periodic Postretirement Benefit Cost. Our results of operations included the following impacts associated with the defined benefit plans: (i) a charge for service rendered by employees; (ii) a charge for accretion of interest; (iii) a benefit for the expected return on plan assets; (iv) amortization of prior service costs associated with plan amendments; and (v) amortization of net actuarial differences. The following table presents the components of Net periodic postretirement benefit cost relating to the defined benefit plans (in millions of dollars): Pension Plans OPEB Salaried VEBA Quarter Ended June 30, Quarter Ended June 30, Quarter Ended June 30, 2024 2023 2024 2023 2024 2023 Service cost $ 1.1 $ 0.8 $ 0.2 $ 0.2 $ — $ — Interest cost 0.4 0.3 0.9 0.9 0.6 0.7 Expected return on plan assets ( 0.4 ) ( 0.2 ) — — ( 0.6 ) ( 0.5 ) Amortization of prior service cost 1 0.1 0.1 — — 0.7 1.3 Amortization of net actuarial gain — — ( 0.2 ) ( 0.3 ) — — Total net periodic postretirement benefit cost $ 1.2 $ 1.0 $ 0.9 $ 0.8 $ 0.7 $ 1.5 Pension Plans OPEB Salaried VEBA Six Months Ended June 30, Six Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 2024 2023 Service cost $ 2.0 $ 1.8 $ 0.5 $ 0.5 $ — $ — Interest cost 0.8 0.6 1.7 1.7 1.1 1.4 Expected return on plan assets ( 0.7 ) ( 0.5 ) — — ( 1.1 ) ( 1.1 ) Amortization of prior service cost 1 0.3 0.1 — — 0.2 2.5 Amortization of net actuarial gain — — ( 0.5 ) ( 0.6 ) — — Total net periodic postretirement benefit cost $ 2.4 $ 2.0 $ 1.7 $ 1.6 $ 0.2 $ 2.8 1. We amortize prior service cost on a straight-line basis over the average remaining years of service of the active plan participants.

Restructuring

Restructuring	6 Months Ended
	Jun. 30, 2024
Restructuring and Related Activities [Abstract]
Restructuring	4. Restructuring 2024 Restructuring Plan. During the quarter, we initiated a plan to exit our soft alloy aluminum extrusion facility located in Sherman, Texas (“2024 Restructuring Plan”). As a result, we recorded a charge of $ 6.8 million during the quarter consisting of a $ 4.6 million multiemployer pension obligation which is expected to be paid in 2027 and a $ 2.2 million charge for severance, related benefits, and other costs, to be substantially paid by December 31, 2024. As of June 30, 2024, the total estimated costs related to the 2024 Restructuring Plan are expected to range from $ 7.0 million to $ 10.0 million. The costs are recorded within Restructuring costs in our Statements of Consolidated Income. The following table summarizes activity relating to the 2024 Restructuring Plan liabilities (in millions of dollars): BALANCE, March 31, 2024 $ — Restructuring costs 6.8 Costs paid or otherwise settled 1 ( 0.6 ) BALANCE, June 30, 2024 $ 6.2 1. Cash paid during the quarter ended June 30, 2024 was $ 0.6 million. 2022 Restructuring Plan. During 2022, we relocated our corporate headquarters from Foothill Ranch, California (“Foothill Ranch”) to Franklin, Tennessee (“Franklin”). In conjunction with the relocation, we initiated a restructuring plan during the quarter ended December 31, 2022, which consisted primarily of employee retention benefits aimed at incentivizing Foothill Ranch employees to assist with the buildout of the new corporate function in Franklin (“2022 Restructuring Plan”). We incurred total restructuring costs of $ 7.4 million related to the 2022 Restructuring Plan, which consisted of employee-related costs and office rent within Restructuring costs in our Statements of Consolidated Income. We completed the 2022 Restructuring Plan as of June 30, 2024. The following table summarizes activity relating to the 2022 Restructuring Plan liabilities (in millions of dollars): BALANCE, December 31, 2023 $ 1.2 Restructuring costs 0.1 Costs paid or otherwise settled 1 ( 1.2 ) BALANCE, March 31, 2024 0.1 Restructuring costs — Costs paid or otherwise settled 1 ( 0.1 ) BALANCE, June 30, 2024 $ — 1. Cash paid during the quarters ended March 31, 2024 and June 30, 2024 was $ 1.1 million and $ 0.1 million, respectively.

Derivatives, Hedging Programs a

Derivatives, Hedging Programs and Other Financial Instruments	6 Months Ended
	Jun. 30, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives, Hedging Programs and Other Financial Instruments	5. Derivatives, Hedging Programs and Other Financial Instruments Overview. In conducting our business, we enter into derivative transactions, including forward contracts and options, to limit our exposure to: (i) metal price risk related to our sale of fabricated aluminum products and the purchase of metal, including primary, rolling ingot and scrap, or recycled, aluminum, our main raw material, and certain alloys used as raw material for our fabrication operations; (ii) energy price risk related to fluctuating prices of natural gas and electricity used in our production processes; and (iii) foreign currency exchange rate risk related to certain equipment and service agreements with vendors for which payments are due in foreign currency. We do not use derivative financial instruments for trading or other speculative purposes. Hedging transactions are executed centrally on behalf of all of our operations to minimize transaction costs, monitor consolidated net exposures, and allow for increased responsiveness to changes in market factors. Our derivative activities are overseen by a committee (“Hedging Committee”), which is composed of our Chief Executive Officer, Chief Financial Officer, Chief Accounting Officer, Treasurer, Executive Vice President of Manufacturing and other officers and employees selected by the Chief Executive Officer. The Hedging Committee meets regularly to review commodity price exposures, derivative positions and strategy. Management reviews the scope of the Hedging Committee’s activities with our Board of Directors. We are exposed to counterparty credit risk on all of our derivative instruments, which we manage by monitoring the credit quality of our counterparties and allocating our hedging positions among multiple counterparties to limit exposure to any single entity. Our counterparties are major investment grade financial institutions or trading companies, and our hedging transactions are governed by negotiated International Swaps and Derivatives Association Master Agreements, which generally require collateral to be posted by our counterparties above specified credit thresholds which may adjust up or down, based on increases or decreases in counterparty credit ratings. As a result, we believe the risk of loss is remote and contained. The aggregate fair value of our derivative instruments that were in a net liability position was $ 2.3 million and $ 1.0 million at June 30, 2024 and December 31, 2023, respectively, and we had no collateral posted as of those dates. In addition, our firm-price customer sales commitments create incremental customer credit risk related to metal price movements. Under certain circumstances, we mitigate this risk by periodically requiring cash collateral to be posted by our customers, which we classify as deferred revenue and include as a component of Other accrued liabilities. We had no material cash collateral posted by our customers at both June 30, 2024 and December 31, 2023. Cash Flow Hedges We designate as cash flow hedges forward swap contracts for aluminum and energy. Additionally, in the fourth quarter of 2023, we adopted this treatment for Alloying Metals used in our fabrication operations. We also designate as cash flow hedges foreign currency forward contracts for equipment and services for which payments are due in foreign currency. Unrealized gains and losses associated with our cash flow hedges are deferred in Other comprehensive income (loss), net of tax, and reclassified to COGS when such hedges settle or when it is probable that the original forecasted transactions will not occur by the end of the originally specified time period. See Note 8 for the total amount of gain or loss on derivative instruments designated and qualifying as cash flow hedging instruments that was reported in AOCI, as well as the related reclassifications into earnings and tax effects. Cumulative gains and losses related to cash flow hedges are reclassified out of AOCI and recorded within COGS when the associated hedged commodity purchases impact earnings. Aluminum Hedges . Our pricing of fabricated aluminum products is generally intended to lock in our Conversion Revenue (representing our value added from the fabrication process) and to pass through aluminum price fluctuations to our customers. For some of our higher margin products sold on a spot basis, the pass through of aluminum price movements can sometimes lag by as much as several months, with a favorable impact to us when aluminum prices decline and an adverse impact to us when aluminum prices increase. Additionally, in certain instances, we enter into firm-price arrangements with our customers for stipulated volumes to be delivered in the future. Because we generally purchase primary and secondary aluminum on a floating price basis, the lag in passing through aluminum price movements to customers on some of our higher margin products sold on a spot basis and the volume that we have committed to sell to our customers under a firm-price arrangement create aluminum price risk for us. We use third-party hedging instruments to limit exposure to aluminum price risk related to the aluminum pass through lag on some of our products and firm-price customer sales contracts. Alloying Metals Hedges . We are exposed to the risk of fluctuating prices for alloying metals used as raw materials in our fabrication operations. We, from time to time, in the ordinary course of business, enter into hedging transactions and/or physical delivery commitments with third parties to mitigate our risk from fluctuations in certain alloying metals prices that are not passed through pursuant to the terms of our customer contracts. Energy Hedges . We are exposed to the risk of fluctuating prices for natural gas and electricity. We, from time to time, in the ordinary course of business, enter into hedging transactions and/or firm price physical delivery commitments with third parties to mitigate our risk from fluctuations in natural gas and electricity prices that are not passed through pursuant to the terms of our customer contracts. Foreign Currency Hedges. We are exposed to foreign currency exchange rate risk related to certain equipment and service agreements with vendors for which payments are due in foreign currency. We, from time to time, in the ordinary course of business, use foreign currency forward contracts in order to mitigate the exposure to currency exchange rate fluctuations related to these purchases. Non-Designated Hedges of Operational Risks From time to time, we enter into commodity and foreign currency forward contracts that are not designated as hedging instruments to mitigate certain short‑term impacts, as identified. The gain or loss on these commodity and foreign currency derivatives is recognized within COGS and Other (expense) income, net, respectively. Notional Amount of Derivative Contracts The following table summarizes our derivative positions at June 30, 2024: Aluminum Maturity Period Notional Amount of Contracts (mmlbs) Fixed price purchase contracts for LME July 2024 through December 2025 62.4 Fixed price purchase contracts for MWTP July 2024 through December 2025 48.9 Fixed price sale contracts for MWTP July 2024 through September 2024 15.5 Alloying Metals Maturity Period Notional Amount of Contracts (mmlbs) Fixed price purchase contracts July 2024 through December 2026 10.0 Natural Gas Maturity Period Notional Amount of Contracts (mmbtu) Fixed price purchase contracts July 2024 through December 2026 3,240,000 Electricity Maturity Period Notional Amount of Contracts (Mwh) Fixed price purchase contracts July 2024 through December 2024 110,425 Euro Maturity Period Notional Amount of Contracts (EUR) Fixed price forward purchase contracts August 2024 through January 2026 10,856,964 British Pounds Maturity Period Notional Amount of Contracts (GBP) Fixed price forward purchase contracts July 2024 72,266 (Gain) Loss on Derivative Contracts The following table summarizes the amount of (gain) loss on derivative contracts recorded within our Statements of Consolidated Income in COGS (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of hedges are recorded: Cash flow hedges $ 690.5 $ 718.4 $ 1,333.4 $ 1,449.5 (Gain) loss recognized in our Statements of Consolidated Income related to cash flow hedges: Aluminum $ ( 2.7 ) $ 5.2 $ ( 0.7 ) $ 5.7 Alloying Metals ( 0.5 ) — ( 0.5 ) — Natural gas 0.4 0.3 0.7 — Electricity 0.8 — 0.6 — Total (gain) loss recognized in our Statements of Consolidated Income related to cash flow hedges $ ( 2.0 ) $ 5.5 $ 0.1 $ 5.7 Loss recognized in our Statements of Consolidated Income related to non-designated derivatives: Alloying Metals – Unrealized mark-to-market loss $ — $ 0.2 $ — $ 0.1 Electricity – Unrealized mark-to-market loss 2.0 — 2.0 — Electricity (reclassification from AOCI due to forecasted transactions probable of not occurring) 0.2 — 0.2 — Total loss recognized in our Statements of Consolidated Income related to non-designated derivatives $ 2.2 $ 0.2 $ 2.2 $ 0.1 Fair Values of Derivative Contracts The fair values of our derivative contracts are based upon trades in liquid markets. Valuation model inputs can be verified, and valuation techniques do not involve significant judgment. The fair values of such derivatives are classified within Level 2 of the fair value hierarchy. All of our derivative contracts with counterparties are subject to enforceable master netting arrangements. We reflect the fair value of our derivative contracts on a gross basis on our Consolidated Balance Sheets. The following table presents the fair value of our derivative assets and liabilities (in millions of dollars): As of June 30, 2024 As of December 31, 2023 Assets Liabilities Net Amount Assets Liabilities Net Amount Aluminum – Fixed price purchase contracts for LME $ 3.4 $ ( 0.7 ) $ 2.7 $ 3.4 $ ( 0.6 ) $ 2.8 Fixed price sale contracts for LME — — — — ( 0.2 ) ( 0.2 ) Fixed price purchase contracts for MWTP 0.3 ( 0.3 ) — 0.4 ( 0.3 ) 0.1 Fixed price sale contracts for MWTP — — — 0.1 ( 0.2 ) ( 0.1 ) Alloying Metals – Fixed price purchase contracts 2.6 — 2.6 0.7 ( 0.1 ) 0.6 Natural gas – Fixed price purchase contracts 0.5 ( 0.7 ) ( 0.2 ) 0.3 ( 0.9 ) ( 0.6 ) Electricity – Fixed price purchase contracts — — — 0.5 ( 0.6 ) ( 0.1 ) Foreign currency – Fixed price forward contracts — ( 0.1 ) ( 0.1 ) 0.5 — 0.5 Total cash flow hedges 6.8 ( 1.8 ) 5.0 5.9 ( 2.9 ) 3.0 Non-Designated Derivatives: Electricity – Fixed price purchase contracts 0.1 ( 2.3 ) ( 2.2 ) — — — Total non-designated derivatives 0.1 ( 2.3 ) ( 2.2 ) — — — Total $ 6.9 $ ( 4.1 ) $ 2.8 $ 5.9 $ ( 2.9 ) $ 3.0 The following table presents the total amounts of derivative assets and liabilities on our Consolidated Balance Sheets (in millions of dollars): As of June 30, 2024 As of December 31, 2023 Derivative assets: Prepaid expenses and other current assets $ 5.4 $ 4.8 Other assets 1.5 1.1 Total derivative assets $ 6.9 $ 5.9 Derivative liabilities: Other accrued liabilities $ ( 3.7 ) $ ( 2.4 ) Long-term liabilities ( 0.4 ) ( 0.5 ) Total derivative liabilities $ ( 4.1 ) $ ( 2.9 ) Fair Value of Other Financial Instruments All Other Financial Assets and Liabilities. We believe that the fair values of our accounts receivable, contract assets, accounts payable and accrued liabilities approximate their respective carrying values due to their short maturities and nominal credit risk.

Debt and Credit Facility

Debt and Credit Facility	6 Months Ended
	Jun. 30, 2024
Debt Disclosure [Abstract]
Debt and Credit Facility	6. Debt and Credit Facility Senior Notes At June 30, 2024 and December 31, 2023 , we had outstanding fixed-rate unsecured Senior Notes with varying maturity dates. The stated interest rates and aggregate principal amounts of our Senior Notes were, respectively: (i) 4.625 % and $ 500.0 million (“4.625% Senior Notes”) and (ii) 4.50 % and $ 550.0 million (“4.50% Senior Notes”). Our Senior Notes do not require us to make any mandatory redemptions or sinking fund payments. The following table summarizes key details of our Senior Notes: Outstanding (in millions of dollars) Issuance Date Maturity Effective Interest Rate As of June 30, 2024 As of December 31, 2023 4.625 % Senior Notes November 2019 March 2028 4.8 % $ 500.0 $ 500.0 4.50 % Senior Notes May 2021 June 2031 4.7 % 550.0 550.0 Total debt 1,050.0 1,050.0 Unamortized issuance costs ( 9.3 ) ( 10.2 ) Total carrying amount $ 1,040.7 $ 1,039.8 The following table presents the fair value of our outstanding Senior Notes, which are Level 1 liabilities (in millions of dollars): As of June 30, 2024 As of December 31, 2023 4.625% Senior Notes $ 467.8 $ 462.4 4.50% Senior Notes $ 487.0 $ 474.1 Revolving Credit Facility In October 2019, we entered into a Revolving Credit Facility. Joining us as borrowers under the Revolving Credit Facility are four of our wholly owned domestic operating subsidiaries: (i) Kaiser Aluminum Investments Company; (ii) Kaiser Aluminum Fabricated Products, LLC; (iii) Kaiser Aluminum Washington, LLC; and (iv) Kaiser Aluminum Warrick, LLC. In April 2022, we entered into Amendment No. 3 to our Revolving Credit Facility. As amended, the Revolving Credit Facility contains a maximum commitment amount of $ 575.0 million (of which up to a maximum of $ 50.0 million may be utilized for letters of credit) and is set to mature in April 2027. Our effective interest rate on outstanding borrowings under the amended Revolving Credit Facility is based on the rates of Base Rate Loans and SOFR Loans (as defined in the amended Revolving Credit Facility). The rate for Base Rate Loans is equal to the prevailing Prime Rate plus 0.25 %, while the rate for SOFR Loans, which are made for one or three month periods, is equal to the Term SOFR Reference Rate (as defined in the amended Revolving Credit Facility) plus 1.35 %. Outstanding borrowings under the Revolving Credit Facility are reported within Long-term debt, net, on our Consolidated Balance Sheets. We had no borrowings under the Revolving Credit Facility during the six months ended June 30, 2024. As of June 30, 2024 and December 31, 2023 , we had no outstanding borrowings under our Revolving Credit Facility. The following table summarizes availability and usage of our Revolving Credit Facility as determined by a borrowing base calculated as of June 30, 2024 (in millions of dollars): Revolving Credit Facility borrowing commitment $ 575.0 Borrowing base availability $ 575.0 Less: Outstanding borrowings under Revolving Credit Facility — Less: Outstanding letters of credit under Revolving Credit Facility ( 27.0 ) Remaining borrowing availability $ 548.0 Interest Expense The following table presents interest expense relating to our Senior Notes and Revolving Credit Facility (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Senior Notes interest expense, including debt issuance cost amortization $ 12.4 $ 12.4 $ 24.8 $ 24.8 Revolving Credit Facility interest expense, including commitment fees and finance cost amortization 0.6 1.0 1.2 1.8 Interest expense on finance lease liabilities 0.2 0.2 0.4 0.3 Interest expense capitalized as construction in progress ( 2.1 ) ( 1.5 ) ( 3.8 ) ( 2.9 ) Total interest expense $ 11.1 $ 12.1 $ 22.6 $ 24.0

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies Commitments. We have a variety of financial commitments, including purchase agreements, forward foreign exchange and forward sales contracts, indebtedness and letters of credit (see Note 5 and Note 6). Environmental Contingencies. We are subject to a number of environmental laws and regulations, potential fines or penalties assessed for alleged breaches of such laws and regulations and potential claims based upon such laws and regulations. We are also subject to legacy environmental contingencies related to activities that occurred at operating facilities prior to July 6, 2006, which represent the majority of our environmental accruals. The status of these environmental contingencies are discussed below. We have established procedures for regularly evaluating environmental loss contingencies. Our environmental accruals represent our undiscounted estimate of costs reasonably expected to be incurred based on presently enacted laws and regulations, currently available facts, existing requirements, existing technology and our assessment of the likely remediation actions to be taken. We continue to pursue remediation activities, primarily to address the historical use of oils containing polychlorinated biphenyls (“PCBs”) at Trentwood. Our remediation efforts are in collaboration with the Washington State Department of Ecology (“Ecology”), to which we submitted a feasibility study in 2012 of remediation alternatives and from which we received permission to begin certain remediation activities pursuant to a signed work order. We have completed a number of sections of the work plan and have received satisfactory completion approval from Ecology on those sections. In cooperation with Ecology, we constructed an experimental treatment facility to determine the treatability and evaluate the feasibility of removing PCBs from ground water under Trentwood. In 2015, we began treatment operations involving a walnut shell filtration system, which we optimized for maximum PCB capture during 2020. Furthermore, based on advancements in technology, we signed an Amended Agreed Order with Ecology in 2020 to evaluate and implement new technologies for PCB removal from groundwater on a pilot basis. The primary technology we are evaluating is Ultraviolet Light Advanced Oxidation Process (the “UV Process”). As the long-term success of the UV Process cannot be reasonably determined at this time, it is possible we may need to make upward adjustments to our related accruals and cost estimates as the long-term results become available. Pursuant to a consent agreement with the Ohio Environmental Protection Agency (“OEPA”), we initiated an investigational study of Newark related to historical on-site waste disposal. During the quarter ended December 31, 2018, we submitted our remedial investigation study to the OEPA for review and approval. The final remedial investigation report was approved by the OEPA during the quarter ended December 31, 2020. We have submitted the Alternate Arrays Document (“AAD”) to the OEPA for review during the quarter ended December 31, 2023. Once the AAD is reviewed and accepted by the OEPA, we plan to submit our feasibility study to the OEPA, which we expect to occur in early 2025 . At June 30, 2024, our environmental accrual of $ 15.3 million represented our estimate of the incremental remediation cost based on: (i) proposed alternatives in the final feasibility study related to Trentwood; (ii) currently available facts with respect to Newark; and (iii) facts related to certain other locations owned or formerly owned by us. In accordance with approved and proposed remediation action plans, we expect that the implementation and ongoing monitoring could occur over a period of 30 or more years. As additional facts are developed, feasibility studies are completed, remediation plans are modified, necessary regulatory approvals for the implementation of remediation are obtained, alternative technologies are developed and/or other factors change, there may be revisions to management’s estimates and actual costs may exceed the current environmental accruals. We believe at this time that it is reasonably possible that undiscounted costs associated with these environmental matters may exceed current accruals by amounts that could be, in the aggregate, up to an estimated $ 11.6 million over the remediation period. It is reasonably possible that our recorded estimate will change in the next 12 months . Other Contingencies. We are party to various lawsuits, claims, investigations and administrative proceedings that arise in connection with past and current operations. We evaluate such matters on a case-by-case basis and our policy is to vigorously contest any such claims we believe are without merit. We accrue for a legal liability when it is both probable that a liability has been incurred and the amount of the loss is reasonably estimable. Quarterly, in addition to when changes in facts and circumstances require it, we review and adjust these accruals to reflect the impacts of negotiations, settlements, rulings, advice of legal counsel and other information and events pertaining to a particular case. While uncertainties are inherent in the final outcome of such matters and it is presently impossible to determine the actual cost that may ultimately be incurred, we believe that we have sufficiently accrued for such matters and that the ultimate resolution of pending matters will not have a material impact on our consolidated financial position, operating results or liquidity.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	6 Months Ended
	Jun. 30, 2024
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	8. Accumulated Other Comprehensive Income (Loss) The following table presents the changes in the accumulated balances for each component of AOCI (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Defined Benefit Plans: Beginning balance $ 10.5 $ 3.5 $ 11.0 $ 2.8 Actuarial gain (loss) arising during the period 1.4 ( 0.6 ) 1.4 ( 0.6 ) Less: income tax (expense) benefit ( 0.3 ) 0.1 ( 0.3 ) 0.1 Net actuarial gain (loss) arising during the period 1.1 ( 0.5 ) 1.1 ( 0.5 ) Prior service cost arising during the period ( 2.2 ) ( 6.6 ) ( 2.2 ) ( 6.6 ) Less: income tax benefit 0.5 1.6 0.5 1.6 Net prior service cost arising during the period ( 1.7 ) ( 5.0 ) ( 1.7 ) ( 5.0 ) Amortization of net actuarial gain 1 ( 0.2 ) ( 0.3 ) ( 0.5 ) ( 0.6 ) Amortization of prior service cost 1 0.8 1.4 0.5 2.6 Less: income tax expense 2 ( 0.1 ) ( 0.2 ) — ( 0.4 ) Net amortization reclassified from AOCI to Net income 0.5 0.9 — 1.6 Other comprehensive loss, net of tax ( 0.1 ) ( 4.6 ) ( 0.6 ) ( 3.9 ) Ending balance $ 10.4 $ ( 1.1 ) $ 10.4 $ ( 1.1 ) Cash Flow Hedges: Beginning balance $ 0.5 $ ( 1.4 ) $ 2.1 $ 0.4 Unrealized gain (loss) on cash flow hedges 6.1 ( 9.0 ) 1.9 ( 11.6 ) Less: income tax (expense) benefit ( 1.4 ) 2.1 ( 0.4 ) 2.7 Net unrealized gain (loss) on cash flow hedges 4.7 ( 6.9 ) 1.5 ( 8.9 ) Reclassification of unrealized (gain) loss upon settlement of cash flow hedges ( 2.0 ) 5.5 0.1 5.7 Reclassification due to forecasted transactions probable of not occurring 0.2 — 0.2 — Less: income tax benefit (expense) 2 0.4 ( 1.3 ) ( 0.1 ) ( 1.3 ) Net (gain) loss reclassified from AOCI to Net income ( 1.4 ) 4.2 0.2 4.4 Other comprehensive income (loss), net of tax 3.3 ( 2.7 ) 1.7 ( 4.5 ) Ending balance 3 $ 3.8 $ ( 4.1 ) $ 3.8 $ ( 4.1 ) Total AOCI ending balance $ 14.2 $ ( 5.2 ) $ 14.2 $ ( 5.2 ) 1. Amounts amortized out of AOCI related to pension and other postretirement benefits were included within Net periodic postretirement benefit cost (see Note 3 ). 2. Income tax amounts reclassified out of AOCI were included as a component of Income tax provision. 3. As of June 30, 2024, we estimate a net mark-to-market gain before tax of $ 3.9 million in AOCI will be reclassified into Net income upon settlement within the next 12 months.

Other (Expense) Income, Net

Other (Expense) Income, Net	6 Months Ended
	Jun. 30, 2024
Other Income and Expenses [Abstract]
Other (Expense) Income, Net	9. Other (Expense) Income, Net The following table presents the components of Other (expense) income, net (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Interest income $ 1.2 $ 0.2 $ 2.1 $ 0.6 Net periodic postretirement benefit cost ( 1.5 ) ( 1.9 ) ( 1.8 ) ( 3.9 ) Unrealized gain on equity securities 0.1 0.2 0.3 0.3 (Loss) gain on disposition of property, plant and equipment ( 0.3 ) ( 0.8 ) ( 0.5 ) 14.2 Gain on business interruption insurance recoveries 1 — — 10.5 — All other, net — ( 0.2 ) ( 0.2 ) ( 0.1 ) Other (expense) income, net $ ( 0.5 ) $ ( 2.5 ) $ 10.4 $ 11.1 1. Represents advances against business interruption insurance claims received by the Company as of June 30, 2024 . We recognize such advances in the period in which the insurance proceeds are received or become realizable. Supply Chain Financing . We are party to several supply chain financing arrangements, in which we may sell certain of our customers’ trade accounts receivable to such customers’ financial institutions without recourse. During the quarter and six months ended June 30, 2024, we sold trade accounts receivable totaling $ 265.3 million and $ 532.4 million , respectively, related to these supply chain financing arrangements, of which our customers’ financial institutions applied discount fees totaling $ 6.5 million and $ 12.8 million , respectively. During the quarter and six months ended June 30, 2023, we sold trade accounts receivable totaling $ 323.4 million and $ 626.6 million , respectively, related to these supply chain financing arrangements, of which our customers’ financial institutions applied discount fees totaling $ 8.0 million and $ 15.2 million , respectively. To the extent discount fees related to the sale of trade accounts receivable under supply chain financing arrangements are not reimbursed by our customers, they are included in Other (expense) income, net. As of June 30, 2024 , we had been and/or expected to be substantially reimbursed by our customers for these discount fees, in accordance with the underlying sales agreements.

Income Tax Matters

Income Tax Matters	6 Months Ended
	Jun. 30, 2024
Income Tax Disclosure [Abstract]
Income Tax Matters	10. Income Tax Matters The following table presents the income tax provision by region (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Domestic $ ( 0.2 ) $ ( 2.5 ) $ ( 7.2 ) $ ( 7.0 ) Foreign ( 0.6 ) ( 0.5 ) ( 1.1 ) ( 0.9 ) Total $ ( 0.8 ) $ ( 3.0 ) $ ( 8.3 ) $ ( 7.9 ) The income tax provision for the quarters ended June 30, 2024 and June 30, 2023 was $ 0.8 million and $ 3.0 million , respectively, reflecting an effective tax rate of 21 % and 14 %, respectively. The difference between the effective tax rate and the projected blended statutory tax rate for the quarter ended June 30, 2024 was primarily due to: (i) a decrease of 9 % related to Federal research and development credits; (ii) a decrease of 4 % related to state tax adjustments for certain state net operating losses; and (iii) a decrease of 3 % for excess tax benefits from stock-based compensation, partially offset by: (i) an increase of 8 % related to non-deductible compensation expense; (ii) an increase of 3 % related to foreign withholding tax; (iii) an increase of 1 % related to foreign taxes; and (iv) an increase of 1 % related to other permanent items. The difference between the effective tax rate and the projected blended statutory tax rate for the quarter ended June 30, 2023 was primarily due to a decrease of 13 % related to Federal research and development and state tax credits, partially offset by: (i) an increase of 1 % related to non-deductible compensation expense; (ii) an increase of 1 % related to foreign withholding tax; and (iii) an increase of 1 % for the recognition of excess book benefits from stock-based compensation. The income tax provision for the six months ended June 30, 2024 and 2023 was $ 8.3 million and $ 7.9 million , respectively, reflecting an effective tax rate of 23 % and 19 %, respectively. There was no material difference between the effective tax rate and the blended statutory tax rate for the six months ended June 30, 2024. The difference between the effective tax rate and the projected blended statutory tax rate for the six months ended June 30, 2023 was primarily due to a decrease of 9 % related to Federal research and development and state tax credits, partially offset by: (i) an increase of 1 % related to non-deductible compensation expense and (ii) an increase of 1 % related to foreign withholding tax. Our gross unrecognized benefits relating to uncertain tax positions were $ 7.2 million and $ 6.5 million at June 30, 2024 and December 31, 2023 , respectively, of which, $ 7.2 million and $ 6.5 million would be recorded through our income tax provision and thus, impact the effective tax rate at June 30, 2024 and December 31, 2023, respectively, if the gross unrecognized tax benefits were to be recognized. We do not expect our gross unrecognized tax benefits to significantly change within the next 12 months.

Earnings Per Share

Earnings Per Share	6 Months Ended
	Jun. 30, 2024
Earnings Per Share [Abstract]
Earnings Per Share	11. Earnings Per Share Basic net income per share is computed by dividing distributed and undistributed net income allocable to common shares by the weighted-average number of common shares outstanding during the app licable period. The basic weighted-average number of common shares outstanding during the period excludes non-vested share-based payment awards. Basic and diluted net income per share was calculated under the two-class method for the quarter and six months ended June 30, 2024 and the treasury method for the quarter and six months ended June 30, 2023, which was more dilutive than the two-class method. The following table sets forth the computation of basic and diluted net income per share (in millions of dollars, except share and per share amounts): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Numerator: Net income available to common shareholders 1 $ 3.1 $ 18.3 $ 27.7 $ 34.2 Denominator – Weighted-average common shares outstanding (in thousands): Basic 16,072 15,974 16,050 15,957 Add: dilutive effect of non-vested common shares, restricted stock units and performance shares 2 326 109 271 133 Diluted 16,398 16,083 16,321 16,090 Net income per common share, Basic: $ 0.19 $ 1.14 $ 1.72 $ 2.14 Net income per common share, Diluted: $ 0.19 $ 1.14 $ 1.69 $ 2.12 1. Represents Net income less distributed and undistributed earnings allocated to non-vested RSAs that contain non-forfeitable rights to dividends. 2. Quantities in the following discussion are denoted in whole shares. During the quarter and six months ended June 30, 2024, approximately 170 and 370 shares, respectively, were excluded from the weighted-average diluted shares computation as their inclusion would have been anti‑dilutive. For the quarter and six months ended June 30, 2023, approximately 42,000 and 16,000 shares, respectively, were excluded from the weighted-average diluted shares computation as their inclusion would have been anti‑dilutive.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	6 Months Ended
	Jun. 30, 2024
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	12. Supplemental Cash Flow Information Six Months Ended June 30, 2024 2023 (In millions of dollars) Interest paid $ 21.0 $ 22.4 Non-cash investing and financing activities (included in Accounts payable): Unpaid purchases of property and equipment $ 32.5 $ 15.9 Supplemental lease disclosures: Operating lease liabilities arising from obtaining operating lease assets $ 0.5 $ 2.6 Cash paid for amounts included in the measurement of operating lease liabilities $ 4.0 $ 4.7 Finance lease liabilities arising from obtaining finance lease assets $ 2.0 $ 9.1 As of June 30, 2024 2023 (In millions of dollars) Components of cash, cash equivalents and restricted cash: Cash and cash equivalents $ 70.4 $ 19.8 Restricted cash included in Other assets 1 18.3 18.6 Total cash, cash equivalents and restricted cash presented on our Statements of Consolidated Cash Flows $ 88.7 $ 38.4 1. We are required to keep on deposit certain amounts that are pledged or held as collateral relating to workers’ compensation and other agreements. We account for such deposits as restricted cash. From time to time, such restricted funds could be returned to us or we could be required to pledge additional cash.

Business, Product and Geographi

Business, Product and Geographical Area Information	6 Months Ended
	Jun. 30, 2024
Segment Reporting [Abstract]
Business, Product and Geographical Area Information	13. Business, Product, and Geographical Area Information Our primary line of business is the production of semi-fabricated specialty aluminum mill products, such as plate and sheet, bare and coated coils, and extruded and drawn products, primarily used in our Aero/HS Products, Packaging, GE Products, Automotive Extrusions, and Other products end markets. We operate production facilities in the United States and Canada. Our chief operating decision maker reviews and evaluates our business as a single operating segment. The following table presents Net sales by end market applications and by timing of control transfer (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Net sales: Aero/HS Products $ 226.1 $ 225.1 $ 446.6 $ 439.1 Packaging 312.4 354.7 610.5 708.9 GE Products 162.6 159.4 315.6 321.5 Automotive Extrusions 69.7 68.4 133.2 139.2 Other products 2.6 6.5 5.0 13.0 Total net sales $ 773.4 $ 814.1 $ 1,510.9 $ 1,621.7 Timing of revenue recognition: Products transferred at a point in time $ 591.8 $ 622.6 $ 1,161.2 $ 1,247.4 Products transferred over time 181.6 191.5 349.7 374.3 Total net sales $ 773.4 $ 814.1 $ 1,510.9 $ 1,621.7 The following table presents geographic information for income taxes paid (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Income taxes paid: Domestic $ 0.2 $ 0.2 $ 0.2 $ 0.3 Foreign 0.6 — 2.2 0.2 Total income taxes paid $ 0.8 $ 0.2 $ 2.4 $ 0.5

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2024
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent Events Dividend Declaration. On July 15, 2024 , we announced that our Board of Directors declared a quarterly cash dividend of $ 0.77 per common share. As such, we expect to pay approximately $ 12.7 million (including dividend equivalents) on or about August 15, 2024 to stockholders of record and the holders of certain restricted stock units at the close of business on July 25, 2024 .

Basis of Presentation and Rec_2

Basis of Presentation and Recent Accounting Pronouncements (Policies)	6 Months Ended
	Jun. 30, 2024
Accounting Policies [Abstract]
Principles of Consolidation and Basis of Presentation	Principles of Consolidation and Basis of Presentation. The accompanying unaudited consolidated financial statements include the accounts of our wholly owned subsidiaries and are prepared in accordance with GAAP and the rules and regulations of the SEC applicable for interim periods and, therefore, do not include all information and footnotes required by GAAP for complete financial statements. In management’s opinion, all adjustments (which include normal recurring adjustments) considered necessary for a fair presentation have been included. We have reclassified certain items in prior periods to conform to current classifications. The results of operations for our interim periods are not necessarily indicative of the results of operations that may be achieved for the entire 2024 fiscal year. The financial information as of December 31, 2023 is derived from our audited consolidated financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2023 .
Use of Estimates in the Preparation of Financial Statements	Use of Estimates in the Preparation of Financial Statements. The preparation of financial statements in accordance with GAAP requires the use of estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities known to exist as of the date the financial statements are published and the reported amounts of revenues and expenses during the reporting period. Uncertainties with respect to such estimates and assumptions are inherent in the preparation of our consolidated financial statements; accordingly, it is possible that the actual results could differ from these estimates and assumptions, which could have a material effect on the reported amounts of our consolidated financial position and results of operations.
Supply Chain Financing	Supply Chain Financing . We are party to several supply chain financing arrangements, in which we may sell certain of our customers’ trade accounts receivable to such customers’ financial institutions without recourse. During the quarter and six months ended June 30, 2024, we sold trade accounts receivable totaling $ 265.3 million and $ 532.4 million , respectively, related to these supply chain financing arrangements, of which our customers’ financial institutions applied discount fees totaling $ 6.5 million and $ 12.8 million , respectively. During the quarter and six months ended June 30, 2023, we sold trade accounts receivable totaling $ 323.4 million and $ 626.6 million , respectively, related to these supply chain financing arrangements, of which our customers’ financial institutions applied discount fees totaling $ 8.0 million and $ 15.2 million , respectively. To the extent discount fees related to the sale of trade accounts receivable under supply chain financing arrangements are not reimbursed by our customers, they are included in Other (expense) income, net. As of June 30, 2024 , we had been and/or expected to be substantially reimbursed by our customers for these discount fees, in accordance with the underlying sales agreements.
Accounting Pronouncements Issued But Not Yet Adopted	Accounting Pronouncements Issued But Not Yet Adopted Disclosure Improvements. In October 2023, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2023-06 (“ASU 2023-06”), Codification Amendments in Response to the SEC’s Disclosure Update and Simplification Initiative. The guidance amends GAAP to reflect updates and simplifications to certain disclosure requirements referred to the FASB by the SEC. The amendments in ASU 2023-06 will become effective on the date which the SEC’s removal of the related disclosure becomes effective. If by June 30, 2027, the SEC does not remove the related disclosure, the pending amendment will be removed from ASC 2023-06 and it will not be effective. Adoption of ASU 2023-06 is expected to modify the disclosure and presentation requirements only and is not expected to have a material impact on our consolidated financial statements. Segment Reporting. In November 2023, the FASB issued ASU No. 2023-07 (“ASU 2023-07”), Improvements to Reportable Segment Disclosures. The guidance primarily will require enhanced disclosures about significant segment expenses. All disclosure requirements under ASU 2023-07 and existing segment disclosures in ASC 280, Segment Reporting are also required for public entities with a single reportable segment. The amendments in ASU 2023-07 are effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024, with early adoption permitted. A retrospective approach is required to be applied to all prior periods presented in the financial statements. We plan to adopt the provisions of ASU 2023-07 in the fourth quarter of fiscal 2024 and continue to evaluate the disclosure requirements related to the new standard. Income Taxes. In December 2023, the FASB issued ASU No. 2023-09 (“ASU 2023-09”), Improvements to Income Tax Disclosures. The guidance is intended to improve income tax disclosure requirements by requiring (i) consistent categories and greater disaggregation of information in the rate reconciliation and (ii) the disaggregation of income taxes paid by jurisdiction. The guidance makes several other changes to the income tax disclosure requirements. The amendments in ASU 2023-09 are effective for fiscal years beginning after December 15, 2024, with early adoption permitted, and is required to be applied prospectively with the option of retrospective application. We plan to adopt the provisions of ASU 2023-09 in the fourth quarter of fiscal 2025 and continue to evaluate the disclosure requirements related to the new standard.

Supplemental Balance Sheet In_2

Supplemental Balance Sheet Information (Tables)	6 Months Ended
	Jun. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Supplemental Balance Sheet Information	As of June 30, 2024 As of December 31, 2023 (In millions of dollars) Trade Receivables, Net Billed trade receivables $ 370.9 $ 325.8 Allowance for doubtful receivables ( 0.8 ) ( 0.6 ) Trade receivables, net $ 370.1 $ 325.2 Inventories 1 Finished products $ 72.1 $ 89.3 Work-in-process 210.2 210.8 Raw materials 148.0 161.5 Operating supplies 16.6 15.6 Inventories $ 446.9 $ 477.2 Property, Plant and Equipment, Net Land and improvements $ 37.2 $ 38.0 Buildings and leasehold improvements 241.6 238.4 Machinery and equipment 1,279.7 1,265.3 Construction in progress 240.1 173.7 Property, plant and equipment, gross 1,798.6 1,715.4 Accumulated depreciation and amortization ( 715.5 ) ( 663.7 ) Land held for sale 1.5 0.4 Property, plant and equipment, net $ 1,084.6 $ 1,052.1 Other Assets Assets to be conveyed associated with Warrick acquisition $ 56.8 $ 56.8 Restricted cash – Note 12 18.3 18.3 Long-term replacement parts 17.3 16.7 Other 26.6 25.9 Other assets $ 119.0 $ 117.7 Other Accrued Liabilities Uncleared cash disbursements $ 20.0 $ 15.7 Accrued income taxes and other taxes payable 10.8 9.5 Accrued annual contribution to Salaried VEBA — 1.1 Accrued interest 9.9 9.9 Short-term environmental accrual – Note 7 0.5 2.8 Current operating lease liabilities 7.2 8.0 Current finance lease liabilities 2.5 2.1 Other – Note 5 14.8 15.2 Other accrued liabilities $ 65.7 $ 64.3 Long-Term Liabilities Workers' compensation accrual $ 29.7 $ 29.9 Long-term environmental accrual – Note 7 14.8 14.2 Other long-term liabilities 43.8 37.6 Long-term liabilities $ 88.3 $ 81.7 1. At June 30, 2024 and December 31, 2023, the current cost of our inventory exceeded its stated last-in, first-out (“LIFO”) value by $ 83.5 million and $ 56.0 million , respectively.

Employee Benefits (Tables)

Employee Benefits (Tables)	6 Months Ended
	Jun. 30, 2024
Retirement Benefits [Abstract]
Schedule of Total Expense Related to Benefit Plans	The following table presents the total expense related to all postretirement benefit plans (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Defined contribution plans 1 $ 4.2 $ 4.3 $ 10.0 $ 10.1 Deferred compensation plan 2 — 0.4 0.7 0.6 Multiemployer pension plans 1 1.5 1.4 3.0 2.8 Net periodic postretirement benefit cost relating to defined benefit plans 2,3 2.8 3.3 4.3 6.4 Total $ 8.5 $ 9.4 $ 18.0 $ 19.9 1. Substantially all of these charges related to employee benefits are in COGS with the remaining balance in Selling, general, administrative, research, and development (“SG&A and R&D”) within our Statements of Consolidated Income. 2. Deferred compensation plan expense and the current service cost component of Net periodic postretirement benefit cost relating to Salaried VEBA are included within our Statements of Consolidated Income in SG&A and R&D for all periods presented. All other components of Net periodic postretirement benefit cost relating to Salaried VEBA are included within Other (expense) income, net, on our Statements of Consolidated Income. 3. The current service cost component of Net periodic postretirement benefit cost relating to both the pension plans and the OPEB plan are included within our Statements of Consolidated Income in COGS for all periods presented. All other components of Net periodic postretirement benefit cost relating to both the pension plans and the OPEB plan are included within Other (expense) income, net, on our Statements of Consolidated Income.
Schedule of Net Benefit Costs	The following table presents the components of Net periodic postretirement benefit cost relating to the defined benefit plans (in millions of dollars): Pension Plans OPEB Salaried VEBA Quarter Ended June 30, Quarter Ended June 30, Quarter Ended June 30, 2024 2023 2024 2023 2024 2023 Service cost $ 1.1 $ 0.8 $ 0.2 $ 0.2 $ — $ — Interest cost 0.4 0.3 0.9 0.9 0.6 0.7 Expected return on plan assets ( 0.4 ) ( 0.2 ) — — ( 0.6 ) ( 0.5 ) Amortization of prior service cost 1 0.1 0.1 — — 0.7 1.3 Amortization of net actuarial gain — — ( 0.2 ) ( 0.3 ) — — Total net periodic postretirement benefit cost $ 1.2 $ 1.0 $ 0.9 $ 0.8 $ 0.7 $ 1.5 Pension Plans OPEB Salaried VEBA Six Months Ended June 30, Six Months Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 2024 2023 Service cost $ 2.0 $ 1.8 $ 0.5 $ 0.5 $ — $ — Interest cost 0.8 0.6 1.7 1.7 1.1 1.4 Expected return on plan assets ( 0.7 ) ( 0.5 ) — — ( 1.1 ) ( 1.1 ) Amortization of prior service cost 1 0.3 0.1 — — 0.2 2.5 Amortization of net actuarial gain — — ( 0.5 ) ( 0.6 ) — — Total net periodic postretirement benefit cost $ 2.4 $ 2.0 $ 1.7 $ 1.6 $ 0.2 $ 2.8 1. We amortize prior service cost on a straight-line basis over the average remaining years of service of the active plan participants.

Restructuring (Tables)

Restructuring (Tables)	6 Months Ended
	Jun. 30, 2024
2024 Plan
Restructuring Cost and Reserve [Line Items]
Summary of Activity Relating to Restructuring Plan Liabilities	The following table summarizes activity relating to the 2024 Restructuring Plan liabilities (in millions of dollars): BALANCE, March 31, 2024 $ — Restructuring costs 6.8 Costs paid or otherwise settled 1 ( 0.6 ) BALANCE, June 30, 2024 $ 6.2 1. Cash paid during the quarter ended June 30, 2024 was $ 0.6 million.
2022 Plan
Restructuring Cost and Reserve [Line Items]
Summary of Activity Relating to Restructuring Plan Liabilities	The following table summarizes activity relating to the 2022 Restructuring Plan liabilities (in millions of dollars): BALANCE, December 31, 2023 $ 1.2 Restructuring costs 0.1 Costs paid or otherwise settled 1 ( 1.2 ) BALANCE, March 31, 2024 0.1 Restructuring costs — Costs paid or otherwise settled 1 ( 0.1 ) BALANCE, June 30, 2024 $ — 1. Cash paid during the quarters ended March 31, 2024 and June 30, 2024 was $ 1.1 million and $ 0.1 million, respectively.

Derivatives, Hedging Programs_2

Derivatives, Hedging Programs and Other Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Summary of Derivative Positions	The following table summarizes our derivative positions at June 30, 2024: Aluminum Maturity Period Notional Amount of Contracts (mmlbs) Fixed price purchase contracts for LME July 2024 through December 2025 62.4 Fixed price purchase contracts for MWTP July 2024 through December 2025 48.9 Fixed price sale contracts for MWTP July 2024 through September 2024 15.5 Alloying Metals Maturity Period Notional Amount of Contracts (mmlbs) Fixed price purchase contracts July 2024 through December 2026 10.0 Natural Gas Maturity Period Notional Amount of Contracts (mmbtu) Fixed price purchase contracts July 2024 through December 2026 3,240,000 Electricity Maturity Period Notional Amount of Contracts (Mwh) Fixed price purchase contracts July 2024 through December 2024 110,425 Euro Maturity Period Notional Amount of Contracts (EUR) Fixed price forward purchase contracts August 2024 through January 2026 10,856,964 British Pounds Maturity Period Notional Amount of Contracts (GBP) Fixed price forward purchase contracts July 2024 72,266 (Gain)
Summary of (Gain) Loss Associated with Derivative Contracts	The following table summarizes the amount of (gain) loss on derivative contracts recorded within our Statements of Consolidated Income in COGS (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Total of income and expense line items presented in our Statements of Consolidated Income in which the effects of hedges are recorded: Cash flow hedges $ 690.5 $ 718.4 $ 1,333.4 $ 1,449.5 (Gain) loss recognized in our Statements of Consolidated Income related to cash flow hedges: Aluminum $ ( 2.7 ) $ 5.2 $ ( 0.7 ) $ 5.7 Alloying Metals ( 0.5 ) — ( 0.5 ) — Natural gas 0.4 0.3 0.7 — Electricity 0.8 — 0.6 — Total (gain) loss recognized in our Statements of Consolidated Income related to cash flow hedges $ ( 2.0 ) $ 5.5 $ 0.1 $ 5.7 Loss recognized in our Statements of Consolidated Income related to non-designated derivatives: Alloying Metals – Unrealized mark-to-market loss $ — $ 0.2 $ — $ 0.1 Electricity – Unrealized mark-to-market loss 2.0 — 2.0 — Electricity (reclassification from AOCI due to forecasted transactions probable of not occurring) 0.2 — 0.2 — Total loss recognized in our Statements of Consolidated Income related to non-designated derivatives $ 2.2 $ 0.2 $ 2.2 $ 0.1
Schedule of Fair Value of Derivative Assets and Liabilities	The following table presents the fair value of our derivative assets and liabilities (in millions of dollars): As of June 30, 2024 As of December 31, 2023 Assets Liabilities Net Amount Assets Liabilities Net Amount Aluminum – Fixed price purchase contracts for LME $ 3.4 $ ( 0.7 ) $ 2.7 $ 3.4 $ ( 0.6 ) $ 2.8 Fixed price sale contracts for LME — — — — ( 0.2 ) ( 0.2 ) Fixed price purchase contracts for MWTP 0.3 ( 0.3 ) — 0.4 ( 0.3 ) 0.1 Fixed price sale contracts for MWTP — — — 0.1 ( 0.2 ) ( 0.1 ) Alloying Metals – Fixed price purchase contracts 2.6 — 2.6 0.7 ( 0.1 ) 0.6 Natural gas – Fixed price purchase contracts 0.5 ( 0.7 ) ( 0.2 ) 0.3 ( 0.9 ) ( 0.6 ) Electricity – Fixed price purchase contracts — — — 0.5 ( 0.6 ) ( 0.1 ) Foreign currency – Fixed price forward contracts — ( 0.1 ) ( 0.1 ) 0.5 — 0.5 Total cash flow hedges 6.8 ( 1.8 ) 5.0 5.9 ( 2.9 ) 3.0 Non-Designated Derivatives: Electricity – Fixed price purchase contracts 0.1 ( 2.3 ) ( 2.2 ) — — — Total non-designated derivatives 0.1 ( 2.3 ) ( 2.2 ) — — — Total $ 6.9 $ ( 4.1 ) $ 2.8 $ 5.9 $ ( 2.9 ) $ 3.0 The following table presents the total amounts of derivative assets and liabilities on our Consolidated Balance Sheets (in millions of dollars): As of June 30, 2024 As of December 31, 2023 Derivative assets: Prepaid expenses and other current assets $ 5.4 $ 4.8 Other assets 1.5 1.1 Total derivative assets $ 6.9 $ 5.9 Derivative liabilities: Other accrued liabilities $ ( 3.7 ) $ ( 2.4 ) Long-term liabilities ( 0.4 ) ( 0.5 ) Total derivative liabilities $ ( 4.1 ) $ ( 2.9 )

Debt and Credit Facility (Table

Debt and Credit Facility (Tables)	6 Months Ended
	Jun. 30, 2024
Debt Disclosure [Abstract]
Summary of Senior Notes	The following table summarizes key details of our Senior Notes: Outstanding (in millions of dollars) Issuance Date Maturity Effective Interest Rate As of June 30, 2024 As of December 31, 2023 4.625 % Senior Notes November 2019 March 2028 4.8 % $ 500.0 $ 500.0 4.50 % Senior Notes May 2021 June 2031 4.7 % 550.0 550.0 Total debt 1,050.0 1,050.0 Unamortized issuance costs ( 9.3 ) ( 10.2 ) Total carrying amount $ 1,040.7 $ 1,039.8
Summary of Fair Value of Outstanding Senior Notes	The following table presents the fair value of our outstanding Senior Notes, which are Level 1 liabilities (in millions of dollars): As of June 30, 2024 As of December 31, 2023 4.625% Senior Notes $ 467.8 $ 462.4 4.50% Senior Notes $ 487.0 $ 474.1
Schedule of Availability and Usage of Revolving Credit Facility	The following table summarizes availability and usage of our Revolving Credit Facility as determined by a borrowing base calculated as of June 30, 2024 (in millions of dollars): Revolving Credit Facility borrowing commitment $ 575.0 Borrowing base availability $ 575.0 Less: Outstanding borrowings under Revolving Credit Facility — Less: Outstanding letters of credit under Revolving Credit Facility ( 27.0 ) Remaining borrowing availability $ 548.0
Summary of Interest Expense Relating to Senior Notes and Revolving Credit Facility	The following table presents interest expense relating to our Senior Notes and Revolving Credit Facility (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Senior Notes interest expense, including debt issuance cost amortization $ 12.4 $ 12.4 $ 24.8 $ 24.8 Revolving Credit Facility interest expense, including commitment fees and finance cost amortization 0.6 1.0 1.2 1.8 Interest expense on finance lease liabilities 0.2 0.2 0.4 0.3 Interest expense capitalized as construction in progress ( 2.1 ) ( 1.5 ) ( 3.8 ) ( 2.9 ) Total interest expense $ 11.1 $ 12.1 $ 22.6 $ 24.0

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Jun. 30, 2024
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The following table presents the changes in the accumulated balances for each component of AOCI (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Defined Benefit Plans: Beginning balance $ 10.5 $ 3.5 $ 11.0 $ 2.8 Actuarial gain (loss) arising during the period 1.4 ( 0.6 ) 1.4 ( 0.6 ) Less: income tax (expense) benefit ( 0.3 ) 0.1 ( 0.3 ) 0.1 Net actuarial gain (loss) arising during the period 1.1 ( 0.5 ) 1.1 ( 0.5 ) Prior service cost arising during the period ( 2.2 ) ( 6.6 ) ( 2.2 ) ( 6.6 ) Less: income tax benefit 0.5 1.6 0.5 1.6 Net prior service cost arising during the period ( 1.7 ) ( 5.0 ) ( 1.7 ) ( 5.0 ) Amortization of net actuarial gain 1 ( 0.2 ) ( 0.3 ) ( 0.5 ) ( 0.6 ) Amortization of prior service cost 1 0.8 1.4 0.5 2.6 Less: income tax expense 2 ( 0.1 ) ( 0.2 ) — ( 0.4 ) Net amortization reclassified from AOCI to Net income 0.5 0.9 — 1.6 Other comprehensive loss, net of tax ( 0.1 ) ( 4.6 ) ( 0.6 ) ( 3.9 ) Ending balance $ 10.4 $ ( 1.1 ) $ 10.4 $ ( 1.1 ) Cash Flow Hedges: Beginning balance $ 0.5 $ ( 1.4 ) $ 2.1 $ 0.4 Unrealized gain (loss) on cash flow hedges 6.1 ( 9.0 ) 1.9 ( 11.6 ) Less: income tax (expense) benefit ( 1.4 ) 2.1 ( 0.4 ) 2.7 Net unrealized gain (loss) on cash flow hedges 4.7 ( 6.9 ) 1.5 ( 8.9 ) Reclassification of unrealized (gain) loss upon settlement of cash flow hedges ( 2.0 ) 5.5 0.1 5.7 Reclassification due to forecasted transactions probable of not occurring 0.2 — 0.2 — Less: income tax benefit (expense) 2 0.4 ( 1.3 ) ( 0.1 ) ( 1.3 ) Net (gain) loss reclassified from AOCI to Net income ( 1.4 ) 4.2 0.2 4.4 Other comprehensive income (loss), net of tax 3.3 ( 2.7 ) 1.7 ( 4.5 ) Ending balance 3 $ 3.8 $ ( 4.1 ) $ 3.8 $ ( 4.1 ) Total AOCI ending balance $ 14.2 $ ( 5.2 ) $ 14.2 $ ( 5.2 ) 1. Amounts amortized out of AOCI related to pension and other postretirement benefits were included within Net periodic postretirement benefit cost (see Note 3 ). 2. Income tax amounts reclassified out of AOCI were included as a component of Income tax provision. 3. As of June 30, 2024, we estimate a net mark-to-market gain before tax of $ 3.9 million in AOCI will be reclassified into Net income upon settlement within the next 12 months.

Other (Expense) Income, Net (Ta

Other (Expense) Income, Net (Tables)	6 Months Ended
	Jun. 30, 2024
Other Income and Expenses [Abstract]
Other (Expense) Income, Net	The following table presents the components of Other (expense) income, net (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Interest income $ 1.2 $ 0.2 $ 2.1 $ 0.6 Net periodic postretirement benefit cost ( 1.5 ) ( 1.9 ) ( 1.8 ) ( 3.9 ) Unrealized gain on equity securities 0.1 0.2 0.3 0.3 (Loss) gain on disposition of property, plant and equipment ( 0.3 ) ( 0.8 ) ( 0.5 ) 14.2 Gain on business interruption insurance recoveries 1 — — 10.5 — All other, net — ( 0.2 ) ( 0.2 ) ( 0.1 ) Other (expense) income, net $ ( 0.5 ) $ ( 2.5 ) $ 10.4 $ 11.1 1. Represents advances against business interruption insurance claims received by the Company as of June 30, 2024 . We recognize such advances in the period in which the insurance proceeds are received or become realizable.

Income Tax Matters (Tables)

Income Tax Matters (Tables)	6 Months Ended
	Jun. 30, 2024
Income Tax Disclosure [Abstract]
Income Tax Provision by Region	The following table presents the income tax provision by region (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Domestic $ ( 0.2 ) $ ( 2.5 ) $ ( 7.2 ) $ ( 7.0 ) Foreign ( 0.6 ) ( 0.5 ) ( 1.1 ) ( 0.9 ) Total $ ( 0.8 ) $ ( 3.0 ) $ ( 8.3 ) $ ( 7.9 )

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 2024
Earnings Per Share [Abstract]
Schedule of Calculation of Basic and Diluted Net Income Per Share	The following table sets forth the computation of basic and diluted net income per share (in millions of dollars, except share and per share amounts): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Numerator: Net income available to common shareholders 1 $ 3.1 $ 18.3 $ 27.7 $ 34.2 Denominator – Weighted-average common shares outstanding (in thousands): Basic 16,072 15,974 16,050 15,957 Add: dilutive effect of non-vested common shares, restricted stock units and performance shares 2 326 109 271 133 Diluted 16,398 16,083 16,321 16,090 Net income per common share, Basic: $ 0.19 $ 1.14 $ 1.72 $ 2.14 Net income per common share, Diluted: $ 0.19 $ 1.14 $ 1.69 $ 2.12 1. Represents Net income less distributed and undistributed earnings allocated to non-vested RSAs that contain non-forfeitable rights to dividends. 2. Quantities in the following discussion are denoted in whole shares. During the quarter and six months ended June 30, 2024, approximately 170 and 370 shares, respectively, were excluded from the weighted-average diluted shares computation as their inclusion would have been anti‑dilutive. For the quarter and six months ended June 30, 2023, approximately 42,000 and 16,000 shares, respectively, were excluded from the weighted-average diluted shares computation as their inclusion would have been anti‑dilutive.

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	6 Months Ended
	Jun. 30, 2024
Supplemental Cash Flow Elements [Abstract]
Schedule of Supplemental Cash Flow Information	Six Months Ended June 30, 2024 2023 (In millions of dollars) Interest paid $ 21.0 $ 22.4 Non-cash investing and financing activities (included in Accounts payable): Unpaid purchases of property and equipment $ 32.5 $ 15.9 Supplemental lease disclosures: Operating lease liabilities arising from obtaining operating lease assets $ 0.5 $ 2.6 Cash paid for amounts included in the measurement of operating lease liabilities $ 4.0 $ 4.7 Finance lease liabilities arising from obtaining finance lease assets $ 2.0 $ 9.1 As of June 30, 2024 2023 (In millions of dollars) Components of cash, cash equivalents and restricted cash: Cash and cash equivalents $ 70.4 $ 19.8 Restricted cash included in Other assets 1 18.3 18.6 Total cash, cash equivalents and restricted cash presented on our Statements of Consolidated Cash Flows $ 88.7 $ 38.4 1. We are required to keep on deposit certain amounts that are pledged or held as collateral relating to workers’ compensation and other agreements. We account for such deposits as restricted cash. From time to time, such restricted funds could be returned to us or we could be required to pledge additional cash.

Business, Product and Geograp_2

Business, Product and Geographical Area Information (Tables)	6 Months Ended
	Jun. 30, 2024
Segment Reporting [Abstract]
Schedule of Net Sales by End Market Segment Applications	The following table presents Net sales by end market applications and by timing of control transfer (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Net sales: Aero/HS Products $ 226.1 $ 225.1 $ 446.6 $ 439.1 Packaging 312.4 354.7 610.5 708.9 GE Products 162.6 159.4 315.6 321.5 Automotive Extrusions 69.7 68.4 133.2 139.2 Other products 2.6 6.5 5.0 13.0 Total net sales $ 773.4 $ 814.1 $ 1,510.9 $ 1,621.7 Timing of revenue recognition: Products transferred at a point in time $ 591.8 $ 622.6 $ 1,161.2 $ 1,247.4 Products transferred over time 181.6 191.5 349.7 374.3 Total net sales $ 773.4 $ 814.1 $ 1,510.9 $ 1,621.7
Schedule of Income Taxes Paid by Geographical Area	The following table presents geographic information for income taxes paid (in millions of dollars): Quarter Ended June 30, Six Months Ended June 30, 2024 2023 2024 2023 Income taxes paid: Domestic $ 0.2 $ 0.2 $ 0.2 $ 0.3 Foreign 0.6 — 2.2 0.2 Total income taxes paid $ 0.8 $ 0.2 $ 2.4 $ 0.5

Supplemental Balance Sheet In_3

Supplemental Balance Sheet Information - Schedule of Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions		Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023
Trade Receivables, Net
Allowance for doubtful receivables		$ (0.8)	$ (0.6)
Trade receivables, net		370.1	325.2
Inventories
Finished products	[1]	72.1	89.3
Work-in-process	[1]	210.2	210.8
Raw materials	[1]	148	161.5
Operating supplies	[1]	16.6	15.6
Inventories	[1]	446.9	477.2
Property, Plant and Equipment, Net
Land and improvements		37.2	38
Buildings and leasehold improvements		241.6	238.4
Machinery and equipment		1,279.7	1,265.3
Construction in progress		240.1	173.7
Property, plant and equipment, gross		1,798.6	1,715.4
Accumulated depreciation and amortization		(715.5)	(663.7)
Land held for sale		1.5	0.4
Property, plant and equipment, net		1,084.6	1,052.1
Other Assets
Assets to be conveyed associated with Warrick acquisition		56.8	56.8
Restricted cash - Note 12		18.3	18.3	$ 18.6
Long-term replacement parts		17.3	16.7
Other		26.6	25.9
Other assets		119	117.7
Other Accrued Liabilities
Uncleared cash disbursements		20	15.7
Accrued income taxes and other taxes payable		10.8	9.5
Accrued annual contribution to Salaried VEBA			1.1
Accrued interest		9.9	9.9
Short-term environmental accrual - Note 7		0.5	2.8
Current operating lease liabilities		7.2	8
Current finance lease liabilities		2.5	2.1
Other - Note 5		14.8	15.2
Other accrued liabilities		65.7	64.3
Long-Term Liabilities
Workers' compensation accrual		29.7	29.9
Long-term environmental accrual - Note 7		14.8	14.2
Other long-term liabilities		43.8	37.6
Long-term liabilities		88.3	81.7
Billed
Trade Receivables, Net
Billed trade receivables		$ 370.9	$ 325.8
[1] At June 30, 2024 and December 31, 2023, the current cost of our inventory exceeded its stated last-in, first-out (“LIFO”) value by $ 83.5 million and $ 56.0 million , respectively.

Supplemental Balance Sheet In_4

Supplemental Balance Sheet Information - Schedule of Supplemental Balance Sheet Information (Parenthetical) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Excess of Replacement or Current Costs over Stated LIFO Value	$ 83.5	$ 56

Employee Benefits - Additional

Employee Benefits - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Warrick Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Actuarial gain due to increase in discount rate	$ 1,400,000
Expected to amortize on a straight-line basis, years	10 years
Projected benefit obligation decreased due to remeasurement	$ 800,000
Increase in pre-tax prior service cost	$ 2,200,000
Benefit obligation, discount rate	5.51%	5.51%		5.51%		5.04%
Expected long-term rate of return on plan assets	$ 0
Description of assumption used to determine benefit obligation				The discount rate assumption used to determine the Warrick Pension Plan benefit obligation was 5.51% at June 30, 2024 compared to 5.04% at December 31, 2023. There was no change to the expected long-term rate of return on plan assets assumption at June 30, 2024 compared to December 31, 2023.
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets		$ 400,000	$ 200,000	$ 700,000	$ 500,000
Pension plan contributions				3,600,000
Employer contributions, remainder of fiscal year	2,200,000	2,200,000		2,200,000
Accrued salaries, wages and related expenses
Defined Benefit Plan Disclosure [Line Items]
Accrued salaries, wages and related expenses	8,700,000	8,700,000		8,700,000
Level 1 | Fair Value, Measurements, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of deferred compensation assets	$ 11,500,000	$ 11,500,000		$ 11,500,000		$ 11,100,000

Employee Benefits - Summary of

Employee Benefits - Summary of Total Expense Related to All Postretirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Net periodic postretirement benefit cost relating to defined benefit plans	$ 1.5	$ 1.9	$ 1.8	$ 3.9
Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost	4.2	4.3	10	10.1
Deferred compensation arrangement with individual, compensation expense		0.4	0.7	0.6
Multiemployer plan, contributions by employer	1.5	1.4	3	2.8
Net periodic postretirement benefit cost relating to defined benefit plans	2.8	3.3	4.3	6.4
Total other employee benefit plans	$ 8.5	$ 9.4	$ 18	$ 19.9

Employee Benefits - Summary o_2

Employee Benefits - Summary of Components of Net Periodic Postretirement Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Total net periodic postretirement benefit cost	$ 1.5	$ 1.9	$ 1.8	$ 3.9
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.1	0.8	2	1.8
Interest cost	0.4	0.3	0.8	0.6
Expected return on plan assets	(0.4)	(0.2)	(0.7)	(0.5)
Amortization of prior service cost	0.1	0.1	0.3	0.1
Total net periodic postretirement benefit cost	1.2	1	2.4	2
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.2	0.2	0.5	0.5
Interest cost	0.9	0.9	1.7	1.7
Amortization of net actuarial gain	(0.2)	(0.3)	(0.5)	(0.6)
Total net periodic postretirement benefit cost	0.9	0.8	1.7	1.6
Postretirement Health Coverage | Salaried VEBA
Defined Benefit Plan Disclosure [Line Items]
Interest cost	0.6	0.7	1.1	1.4
Expected return on plan assets	(0.6)	(0.5)	(1.1)	(1.1)
Amortization of prior service cost	0.7	1.3	0.2	2.5
Total net periodic postretirement benefit cost	$ 0.7	$ 1.5	$ 0.2	$ 2.8

Restructuring - Additional Info

Restructuring - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	18 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2024	Mar. 31, 2024
2022 Plan
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 0	$ 0.1		$ 7.4
2024 Plan
Restructuring Cost and Reserve [Line Items]
Restructuring costs	6.8		$ 6.8
Severance charge			2.2
Pension obligation expected to be paid			4.6
2024 Plan | Minimum
Restructuring Cost and Reserve [Line Items]
Total expected estimated costs	7		7
2024 Plan | Maximum
Restructuring Cost and Reserve [Line Items]
Total expected estimated costs	$ 10		$ 10

Restructuring - Summary of Acti

Restructuring - Summary of Activity Relating to Restructuring Plan Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	18 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2024	Mar. 31, 2024
2024 Plan
Restructuring Cost and Reserve [Line Items]
Beginning balance
Restructuring costs	6.8		$ 6.8
Costs paid or otherwise settled	(0.6)
Ending balance	6.2		6.2
2022 Plan
Restructuring Cost and Reserve [Line Items]
Beginning balance	0.1	1.2	$ 1.2
Restructuring costs	0	0.1		7.4
Costs paid or otherwise settled	$ (0.1)	(1.2)
Ending balance		$ 0.1		$ 0.1

Restructuring - Summary of Ac_2

Restructuring - Summary of Activity Relating to Restructuring Plan Liabilities (Parenthetical) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2024	Mar. 31, 2024
2024 Plan
Restructuring Cost and Reserve [Line Items]
Cash Paid	$ 0.6
2022 Plan
Restructuring Cost and Reserve [Line Items]
Cash Paid	$ 0.1	$ 1.1

Derivatives, Hedging Programs_3

Derivatives, Hedging Programs and Other Financial Instruments - Additional Information (Details) - USD ($)	Jun. 30, 2024	Dec. 31, 2023
Derivative [Line Items]
Collateral posted for net derivatives	$ 0	$ 0
Cash collateral posted by customers	0	0
Designated as Hedging Instrument | Purchase
Derivative [Line Items]
Derivative net liability	$ 2,300,000	$ 1,000,000

Derivatives, Hedging Programs_4

Derivatives, Hedging Programs and Other Financial Instruments - Summary of Derivative Positions (Details) - 6 months ended Jun. 30, 2024 Mmlb in Millions	EUR (€) MWh Mmlb MMBTU	GBP (£) MWh Mmlb MMBTU
Purchase | Aluminum
Derivative [Line Items]
Derivative non-monetary notional amount	62.4	62.4
Purchase | Aluminum | Minimum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2024
Purchase | Aluminum | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2025
Purchase | Fixed Price Purchase Contracts for MWTP
Derivative [Line Items]
Derivative non-monetary notional amount	48.9	48.9
Purchase | Fixed Price Purchase Contracts for MWTP | Minimum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2024
Purchase | Fixed Price Purchase Contracts for MWTP | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2025
Purchase | Alloying Metals
Derivative [Line Items]
Derivative non-monetary notional amount	10	10
Purchase | Alloying Metals | Minimum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2024
Purchase | Alloying Metals | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2026
Purchase | Natural Gas
Derivative [Line Items]
Derivative non-monetary notional amount | MMBTU	3,240,000	3,240,000
Purchase | Natural Gas | Minimum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2024
Purchase | Natural Gas | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2026
Purchase | Electricity
Derivative [Line Items]
Derivative non-monetary notional amount | MWh	110,425	110,425
Purchase | Electricity | Minimum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2024
Purchase | Electricity | Maximum
Derivative [Line Items]
Derivative maturity period	Dec. 31, 2024
Purchase | Euro
Derivative [Line Items]
Derivative notional amount | €	€ 10,856,964
Purchase | Euro | Minimum
Derivative [Line Items]
Derivative maturity period	Aug. 31, 2024
Purchase | Euro | Maximum
Derivative [Line Items]
Derivative maturity period	Jan. 31, 2026
Purchase | British Pounds
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2024
Derivative notional amount | £		£ 72,266
Sales | Fixed Price Sale Contracts for MWTP
Derivative [Line Items]
Derivative non-monetary notional amount	15.5	15.5
Sales | Fixed Price Sale Contracts for MWTP | Minimum
Derivative [Line Items]
Derivative maturity period	Jul. 31, 2024
Sales | Fixed Price Sale Contracts for MWTP | Maximum
Derivative [Line Items]
Derivative maturity period	Sep. 30, 2024

Derivatives, Hedging Programs_5

Derivatives, Hedging Programs and Other Financial Instruments - Summary of (Gain) Loss Associated with Derivative Contracts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Derivative Instruments Gain Loss [Line Items]
Total of income and expense line items presented in our Statements of Consolidated Income (Loss) in which the effects of cash flow hedges are recorded	$ 690.5	$ 718.4	$ 1,333.4	$ 1,449.5
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total of income and expense line items presented in our Statements of Consolidated Income (Loss) in which the effects of cash flow hedges are recorded	Total of income and expense line items presented in our Statements of Consolidated Income (Loss) in which the effects of cash flow hedges are recorded	Total of income and expense line items presented in our Statements of Consolidated Income (Loss) in which the effects of cash flow hedges are recorded	Total of income and expense line items presented in our Statements of Consolidated Income (Loss) in which the effects of cash flow hedges are recorded
Loss recognized in our Statements of Consolidated Income - Unrealized mark-to-market loss			$ 2.2
Not Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized in our Statements of Consolidated Income	$ 2.2	$ 0.2	2.2	$ 0.1
Not Designated as Hedging Instrument | Alloying Metals
Derivative Instruments Gain Loss [Line Items]
Loss recognized in our Statements of Consolidated Income - Unrealized mark-to-market loss		0.2		0.1
Not Designated as Hedging Instrument | Electricity
Derivative Instruments Gain Loss [Line Items]
Loss recognized in our Statements of Consolidated Income - Unrealized mark-to-market loss	2		2
Reclassification from AOCI due to forecasted transactions probable of not occurring	0.2		0.2
Cash Flow Hedges
Derivative Instruments Gain Loss [Line Items]
Total of income and expense line items presented in our Statements of Consolidated Income (Loss) in which the effects of cash flow hedges are recorded	690.5	718.4	1,333.4	1,449.5
Cash Flow Hedges | Designated as Hedging Instrument
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized in our Statements of Consolidated Income	(2)	5.5	0.1	5.7
Cash Flow Hedges | Designated as Hedging Instrument | Aluminum
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized in our Statements of Consolidated Income	(2.7)	5.2	(0.7)	$ 5.7
Cash Flow Hedges | Designated as Hedging Instrument | Alloying Metals
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized in our Statements of Consolidated Income	(0.5)		(0.5)
Cash Flow Hedges | Designated as Hedging Instrument | Natural Gas
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized in our Statements of Consolidated Income	0.4	$ 0.3	0.7
Cash Flow Hedges | Designated as Hedging Instrument | Electricity
Derivative Instruments Gain Loss [Line Items]
(Gain) loss recognized in our Statements of Consolidated Income	$ 0.8		$ 0.6

Derivatives, Hedging Programs_6

Derivatives, Hedging Programs and Other Financial Instruments - Schedule of Fair Value of Derivative Financial Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Designated as Hedging Instrument | Purchase
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	$ (2.3)	$ (1)
Fair Value, Measurements, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	6.9	5.9
Liabilities	(4.1)	(2.9)
Fair Value, Measurements, Recurring | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	6.9	5.9
Liabilities	(4.1)	(2.9)
Net Amount	2.8	3
Fair Value, Measurements, Recurring | Level 1 | Not Designated as Hedging Instrument
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0.1
Liabilities	(2.3)
Net Amount	(2.2)
Fair Value, Measurements, Recurring | Level 1 | Not Designated as Hedging Instrument | Purchase | Electricity
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0.1
Liabilities	(2.3)
Net Amount	(2.2)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	6.8	5.9
Liabilities	(1.8)	(2.9)
Net Amount	5	3
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Natural Gas
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0.5	0.3
Liabilities	(0.7)	(0.9)
Net Amount	(0.2)	(0.6)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Aluminum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	3.4	3.4
Liabilities	(0.7)	(0.6)
Net Amount	2.7	2.8
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Fixed Price Purchase Contracts for MWTP
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	0.3	0.4
Liabilities	(0.3)	(0.3)
Net Amount		0.1
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Fixed Price Sale Contracts for MWTP
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets		0.1
Liabilities		(0.2)
Net Amount		(0.1)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Foreign Currency
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets		0.5
Liabilities	(0.1)
Net Amount	(0.1)	0.5
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Alloying Metals
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	2.6	0.7
Liabilities		(0.1)
Net Amount	$ 2.6	0.6
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Purchase | Electricity
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets		0.5
Liabilities		(0.6)
Net Amount		(0.1)
Fair Value, Measurements, Recurring | Cash Flow Hedges | Level 1 | Designated as Hedging Instrument | Sales | Aluminum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities		(0.2)
Net Amount		$ (0.2)

Derivatives, Hedging Programs_7

Derivatives, Hedging Programs and Other Financial Instruments - Schedule of Total Amounts of Derivative Assets and Liabilities on Balance Sheets (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Derivative [Line Items]
Derivative asset current	$ 5.4	$ 4.8
Derivative Asset, Current, Statement of Financial Position [Extensible Enumeration]	Prepaid Expense and Other Assets, Current	Prepaid Expense and Other Assets, Current
Derivative asset noncurrent	$ 1.5	$ 1.1
Derivative Asset, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other Assets, Noncurrent	Other Assets, Noncurrent
Total derivative assets	$ 6.9	$ 5.9
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Assets	Assets
Derivative liabilities current	$ (3.7)	$ (2.4)
Derivative Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Accrued Liabilities, Current	Other Accrued Liabilities, Current
Derivative liabilities noncurrent	$ (0.4)	$ (0.5)
Derivative Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Noncurrent	Other Liabilities, Noncurrent
Total derivative liabilities	$ (4.1)	$ (2.9)
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Liabilities	Liabilities

Debt and Credit Facility (Senio

Debt and Credit Facility (Senior Notes) - Additional Information (Details) - Senior Notes - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Debt instrument aggregate principal amount	$ 1,050	$ 1,050
4.50% Senior Notes
Debt Instrument [Line Items]
Debt instrument contractual rate (percent)	4.50%	4.50%
Debt instrument aggregate principal amount	$ 550	$ 550
4.625% Senior Notes
Debt Instrument [Line Items]
Debt instrument contractual rate (percent)	4.625%	4.625%
Debt instrument aggregate principal amount	$ 500	$ 500

Debt and Credit Facility - Summ

Debt and Credit Facility - Summary of Senior Notes (Details) - Senior Notes - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Total debt	$ 1,050	$ 1,050
Unamortized issuance costs	(9.3)	(10.2)
Total carrying amount	$ 1,040.7	1,039.8
4.50% Senior Notes
Debt Instrument [Line Items]
Issuance Date	May 21, 2021
Debt Instrument, Maturity Date	Jun. 30, 2031
Effective interest rate (percent)	4.70%
Total debt	$ 550	550
4.625% Senior Notes
Debt Instrument [Line Items]
Issuance Date	Nov. 30, 2019
Debt Instrument, Maturity Date	Mar. 31, 2028
Effective interest rate (percent)	4.80%
Total debt	$ 500	$ 500

Debt and Credit Facility - Su_2

Debt and Credit Facility - Summary of Senior Notes (Parenthetical) (Details) - Senior Notes	Jun. 30, 2024	Dec. 31, 2023
4.50% Senior Notes
Debt Instrument [Line Items]
Debt instrument contractual rate (percent)	4.50%	4.50%
4.625% Senior Notes
Debt Instrument [Line Items]
Debt instrument contractual rate (percent)	4.625%	4.625%

Debt and Credit Facility - Su_3

Debt and Credit Facility - Summary of Fair Value of Outstanding Senior Notes (Details) - Senior Notes - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
4.50% Senior Notes
Debt Instrument [Line Items]
Fair value of outstanding senior notes	$ 487	$ 474.1
4.625% Senior Notes
Debt Instrument [Line Items]
Fair value of outstanding senior notes	$ 467.8	$ 462.4

Debt and Credit Facility (Revol

Debt and Credit Facility (Revolving Credit Facility) - Additional Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Dec. 31, 2023	Apr. 30, 2022	Oct. 31, 2019
Amended Credit Agreement
Debt Instrument [Line Items]
Line of credit mature description	As amended, the Revolving Credit Facility contains a maximum commitment amount of $575.0 million (of which up to a maximum of $50.0 million may be utilized for letters of credit) and is set to mature in April 2027.
Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 575
Outstanding borrowings	$ 0	$ 0
Revolving Credit Facility | Amended Credit Agreement
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			$ 575
Revolving Credit Facility | Letter of Credit | Amended Credit Agreement
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity			$ 50
Revolving Credit Facility | Prime Rate
Debt Instrument [Line Items]
Effective interest rate (percent)				0.25%
Revolving Credit Facility | SOFR | Amended Credit Agreement
Debt Instrument [Line Items]
Effective interest rate (percent)				1.35%

Debt and Credit Facility - Sche

Debt and Credit Facility - Schedule of Availability and Usage of Revolving Credit Facility (Details) - Revolving Credit Facility - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Line Of Credit Facility [Line Items]
Revolving Credit Facility borrowing commitment	$ 575
Borrowing base availability	575
Less: Outstanding borrowings under Revolving Credit Facility	0	$ 0
Less: Outstanding letters of credit under Revolving Credit Facility	(27)
Remaining borrowing availability	$ 548

Debt and Credit Facility - Su_4

Debt and Credit Facility - Summary of Interest Expense Relating to Senior Notes and Revolving Credit Facility (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Debt Instrument [Line Items]
Total interest expense	$ 11.1	$ 12.1	$ 22.6	$ 24
Senior Notes and Revolving Credit Facility
Debt Instrument [Line Items]
Interest expense on finance lease liabilities	0.2	0.2	0.4	0.3
Interest expense capitalized as construction in progress	(2.1)	(1.5)	(3.8)	(2.9)
Total interest expense	11.1	12.1	22.6	24
Revolving Credit Facility
Debt Instrument [Line Items]
Revolving Credit Facility interest expense, including commitment fees and finance cost amortization	0.6	1	1.2	1.8
Senior Notes
Debt Instrument [Line Items]
Senior Notes interest expense, including debt issuance cost amortization	$ 12.4	$ 12.4	$ 24.8	$ 24.8

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Millions	6 Months Ended
	Jun. 30, 2024 USD ($)
Environmental Contingency
Estimated final remediation cost feasibility study expected occur year	2025
Environmental accrual	$ 15.3
Expected period related to remediation expenditures for environmental contingencies period	30 years
Potential increase in environmental costs	$ 11.6
Time period within which recorded estimate of its environmental obligation may change	12 months

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended						6 Months Ended
		Jun. 30, 2024		Mar. 31, 2024	Jun. 30, 2023		Mar. 31, 2023	Jun. 30, 2024		Jun. 30, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 664.9		$ 652.2	$ 635.6		$ 631.2	$ 652.2		$ 631.2
Other comprehensive income (loss), net of tax		3.2		(2.1)	(7.3)		(1.1)	1.1		(8.4)
Ending balance		662		664.9	638.1		635.6	662		638.1
Defined Benefit Plans:
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		10.5		11	3.5		2.8	11		2.8
Less: income tax benefit (expense)	[1]	(0.1)			(0.2)					(0.4)
Net (gain) loss reclassified from AOCI to Net income		0.5			0.9					1.6
Other comprehensive income (loss), net of tax		(0.1)			(4.6)			(0.6)		(3.9)
Ending balance		10.4		10.5	(1.1)		3.5	10.4		(1.1)
Defined Benefit Plans: Net Actuarial Gain
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Unrealized gain (loss) on securities		1.4			(0.6)			1.4		(0.6)
Less: income tax (expense) benefit		(0.3)			0.1			(0.3)		0.1
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges		1.1			(0.5)			1.1		(0.5)
Reclassification from AOCI	[2]	(0.2)			(0.3)			(0.5)		(0.6)
Defined Benefit Plans: Net Prior Service (Credit) Cost
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Unrealized gain (loss) on securities		(2.2)			(6.6)			(2.2)		(6.6)
Less: income tax (expense) benefit		0.5			1.6			0.5		1.6
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges		(1.7)			(5)			(1.7)		(5)
Reclassification from AOCI	[2]	0.8			1.4			0.5		2.6
Cash Flow Hedges:
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		0.5		2.1	(1.4)		0.4	2.1		0.4
Unrealized gain (loss) on securities		6.1			(9)			1.9		(11.6)
Less: income tax (expense) benefit		(1.4)			2.1			(0.4)		2.7
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges		4.7			(6.9)			1.5		(8.9)
Reclassification from AOCI		(2)			5.5			0.1		5.7
Reclassification due to forecasted transactions probable of not occurring		0.2						0.2
Less: income tax benefit (expense)		0.4			(1.3)			(0.1)		(1.3)
Net (gain) loss reclassified from AOCI to Net income		(1.4)			4.2			0.2		4.4
Other comprehensive income (loss), net of tax		3.3			(2.7)			1.7		(4.5)
Ending balance		3.8	[3]	0.5	(4.1)	[3]	(1.4)	3.8	[3]	(4.1)	[3]
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		11		13.1	2.1		3.2	13.1		3.2
Other comprehensive income (loss), net of tax		3.2		(2.1)	(7.3)		(1.1)
Ending balance		$ 14.2		$ 11	$ (5.2)		$ 2.1	$ 14.2		$ (5.2)
[1] Income tax amounts reclassified out of AOCI were included as a component of Income tax provision. Amounts amortized out of AOCI related to pension and other postretirement benefits were included within Net periodic postretirement benefit cost (see Note 3 ). As of June 30, 2024, we estimate a net mark-to-market gain before tax of $ 3.9 million in AOCI will be reclassified into Net income upon settlement within the next 12 months.

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2024 USD ($)
Equity [Abstract]
Estimated net mark-to-market loss before tax within next twelve months - cash flow hedges	$ 3.9

Other (Expense) Income, Net - C

Other (Expense) Income, Net - Components of Other income, Net (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Other Income and Expenses [Abstract]
Interest income		$ 1.2	$ 0.2	$ 2.1	$ 0.6
Net periodic postretirement benefit cost		(1.5)	(1.9)	(1.8)	(3.9)
Unrealized gain on equity securities		0.1	0.2	0.3	0.3
(Loss) gain on disposition of property, plant and equipment		(0.3)	(0.8)	(0.5)	14.2
Gain on business interruption insurance recoveries	[1]	0	0	10.5	0
All other, net		0	(0.2)	(0.2)	(0.1)
Other (expense) income, net		$ (0.5)	$ (2.5)	$ 10.4	$ 11.1
[1] Represents advances against business interruption insurance claims received by the Company as of June 30, 2024 . We recognize such advances in the period in which the insurance proceeds are received or become realizable.

Other (Expense) Income, Net - A

Other (Expense) Income, Net - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Other Income and Expenses [Abstract]
Trade accounts receivable sold	$ 265.3	$ 323.4	$ 532.4	$ 626.6
Net discount fees recognized	$ 6.5	$ 8	$ 12.8	$ 15.2

Income Tax Matters - Income Tax

Income Tax Matters - Income Tax Provision by Region (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income Tax Disclosure [Abstract]
Domestic	$ (0.2)	$ (2.5)	$ (7.2)	$ (7)
Foreign	(0.6)	(0.5)	(1.1)	(0.9)
Total	$ (0.8)	$ (3)	$ (8.3)	$ (7.9)

Income Tax Matters - Additional

Income Tax Matters - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Effective Income Tax Rate Reconciliation [Line Items]
Income tax provision	$ 0.8	$ 3	$ 8.3	$ 7.9
Effective tax rate (percent)	21%	14%	23%	19%
Effective income tax rate reconciliation, related to federal research & development credit, percent (decrease)	(9.00%)	(13.00%)		(9.00%)
Effective income tax rate reconciliation, state tax adjustments for certain state net operating losses, percent	(4.00%)
Effective income tax rate reconciliation, foreign withholding tax, percent	3%	1%		1%
Effective income tax rate reconciliation, related to non-deductible compensation expense, percent	8%	1%		1%
Effective income tax rate reconciliation, foreign taxes	1%
Effective income tax rate reconciliation, tax expense (benefit), share-based payment arrangement, percent	(3.00%)	1%
Effective income tax rate reconciliation, other permanent items, percent	1%
Gross unrecognized tax benefits	$ 7.2		$ 7.2		$ 6.5
Gross unrecognized tax benefits that would impact effective tax rate	$ 7.2		$ 7.2		$ 6.5

Earnings Per Share - Schedule o

Earnings Per Share - Schedule of Calculation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Numerator:
Net income available to common shareholders	[1]	$ 3.1	$ 18.3	$ 27.7	$ 34.2
Denominator – Weighted-average common shares outstanding (in thousands):
Basic		16,072	15,974	16,050	15,957
Add: dilutive effect of non-vested common shares, restricted stock units and performance shares	[2]	326	109	271	133
Diluted		16,398	16,083	16,321	16,090
Net income per common share, Basic:		$ 0.19	$ 1.14	$ 1.72	$ 2.14
Net income per common share, Diluted:		$ 0.19	$ 1.14	$ 1.69	$ 2.12
[1] Represents Net income less distributed and undistributed earnings allocated to non-vested RSAs that contain non-forfeitable rights to dividends. Quantities in the following discussion are denoted in whole shares. During the quarter and six months ended June 30, 2024, approximately 170 and 370 shares, respectively, were excluded from the weighted-average diluted shares computation as their inclusion would have been anti‑dilutive. For the quarter and six months ended June 30, 2023, approximately 42,000 and 16,000 shares, respectively, were excluded from the weighted-average diluted shares computation as their inclusion would have been anti‑dilutive.

Earnings Per Share - Schedule_2

Earnings Per Share - Schedule of Calculation of Basic and Diluted Net Income Per Share (Parenthetical) (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share, amount	170	42,000	370	16,000

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information - Schedule of Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Supplemental Cash Flow Elements [Abstract]
Interest paid	$ 21	$ 22.4
Non-cash investing and financing activities (included in Accounts payable):
Unpaid purchases of property and equipment	32.5	15.9
Supplemental Lease Disclosures [Abstract]
Operating lease liabilities arising from obtaining operating lease assets	0.5	2.6
Cash paid for amounts included in the measurement of operating lease liabilities	4	4.7
Finance lease liabilities arising from obtaining finance lease assets	2	9.1
Components of cash, cash equivalents and restricted cash:
Cash and cash equivalents	70.4	19.8	$ 82.4
Restricted cash included in Other assets	18.3	18.6	18.3
Total cash, cash equivalents and restricted cash presented on our Statements of Consolidated Cash Flows	$ 88.7	$ 38.4	$ 100.7	$ 71.3

Business, Product and Geograp_3

Business, Product and Geographical Area Information - Net Sales by End Market Segment Applications (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Net sales:
Net sales	$ 773.4	$ 814.1	$ 1,510.9	$ 1,621.7
Aero/HS Products
Net sales:
Net sales	226.1	225.1	446.6	439.1
Packaging
Net sales:
Net sales	312.4	354.7	610.5	708.9
GE Products
Net sales:
Net sales	162.6	159.4	315.6	321.5
Automotive Extrusions
Net sales:
Net sales	69.7	68.4	133.2	139.2
Other products
Net sales:
Net sales	2.6	6.5	5	13
Products Transferred at a Point in Time
Net sales:
Net sales	591.8	622.6	1,161.2	1,247.4
Products Transferred Over Time
Net sales:
Net sales	$ 181.6	$ 191.5	$ 349.7	$ 374.3

Business, Product and Geograp_4

Business, Product and Geographical Area Information - Schedule of Income Taxes Paid by Geographical Area (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income Taxes Paid By Geographical Area [Line Items]
Income taxes paid	$ 0.8	$ 0.2	$ 2.4	$ 0.5
Domestic
Income Taxes Paid By Geographical Area [Line Items]
Income taxes paid	0.2	0.2	0.2	0.3
Foreign
Income Taxes Paid By Geographical Area [Line Items]
Income taxes paid	$ 0.6	$ 0	$ 2.2	$ 0.2

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
	Jul. 15, 2024	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023
Subsequent Event [Line Items]
Cash dividends declared (in dollars per share)		$ 0.77	$ 0.77	$ 0.77	$ 0.77
Subsequent Events
Subsequent Event [Line Items]
Cash dividends declared (in dollars per share)	$ 0.77
Cash dividends declared	$ 12.7
Cash dividends, declared date	Jul. 15, 2024
Cash dividends, payable date	Aug. 15, 2024
Cash dividends, record date	Jul. 25, 2024